Tank filters placed in series with the lead wires or circuits of active medical devices to enhance MRI compatibility

ABSTRACT

A TANK filter is provided for a lead wire of an active medical device (AMD). The TANK filter includes a capacitor in parallel with an inductor. The parallel capacitor and inductor are placed in series with the lead wire of the AMD, wherein values of capacitance and inductance are selected such that the TANK filter is resonant at a selected frequency. The Q of the inductor may be relatively maximized and the Q of the capacitor may be relatively minimized to reduce the overall Q of the TANK filter to attenuate current flow through the lead wire along a range of selected frequencies. In a preferred form, the TANK filter is integrated into a TIP and/or RING electrode for an active implantable medical device.

BACKGROUND OF THE INVENTION

This invention relates generally to electromagnetic interference (EMI)TANK filter assemblies, particularly of the type used in activeimplantable medical devices (AIMDs) such as cardiac pacemakers,cardioverter defibrillators, neurostimulators and the like, which raisethe impedance of internal electronic or related wiring components of themedical device at selected frequencies in order to reduce or eliminatecurrents induced from undesirable electromagnetic interference (EMI)signals. The invention is also applicable to a wide variety ofcommercial, telecommunications, military and space applications. Thepresent invention is also applicable to a wide range of external medicaldevices, including externally worn drug pumps, EKG/ECG electrodes,neurostimulators, ventricular assist devices and the like. The presentinvention is also applicable to a wide range of probes, catheters,monitoring lead wires and the like that may be temporarily inserted intoor onto a patient or that a patient may be wearing or connected toduring medical diagnostic procedures such as MRI.

Compatibility of cardiac pacemakers, implantable defibrillators andother types of active implantable medical devices with magneticresonance imaging (MRI) and other types of hospital diagnostic equipmenthas become a major issue. If one goes to the websites of the majorcardiac pacemaker manufacturers in the United States, which include St.Jude Medical, Medtronic and Boston Scientific CRM (formerly Guidant),one will see that the use of MRI is generally contra-indicated withpacemakers and implantable defibrillators. A similar contra-indicationis found in the manuals of MRI equipment manufacturers such as Siemens,GE, and Phillips. See also “Safety Aspects of Cardiac Pacemakers inMagnetic Resonance Imaging”, a dissertation submitted to the SwissFederal Institute of Technology Zurich presented by Roger ChristophLüchinger. “Dielectric Properties of Biological Tissues: I. LiteratureSurvey”, by C. Gabriel, S. Gabriel and E. Cortout; “DielectricProperties of Biological Tissues: II. Measurements and the FrequencyRange 0 Hz to 20 GHz”, by S. Gabriel, R. W. Lau and C. Gabriel;“Dielectric Properties of Biological Tissues: III. Parametric Models forthe Dielectric Spectrum of Tissues”, by S. Gabriel, R. W. Lau and C.Gabriel; and “Advanced Engineering Electromagnetics, C. A. Balanis,Wiley, 1989, all of which are incorporated herein by reference.

However, an extensive review of the literature indicates that MRI isindeed often used with pacemaker patients, in spite of the contraindications. The safety and feasibility of MRI in patients with cardiacpacemakers is an issue of gaining significance. The effects of MRI onpatients' pacemaker systems have only been analyzed retrospectively insome case reports. There are a number of papers that indicate that MRIon new generation pacemakers can be conducted up to 0.5 Tesla (T). Otherpapers go up to 1.5 T for non-pacemaker dependent patients under highlycontrolled conditions. MRI is one of medicine's most valuable diagnostictools. MRI is, of course, extensively used for imaging, but is alsoincreasingly used for real-time procedures such as interventionalmedicine (surgery). In addition, MRI is used in real time to guideablation catheters, neurostimulator tips, deep brain probes and thelike. An absolute contra-indication for pacemaker patients means thatpacemaker and ICD wearers are excluded from MRI. This is particularlytrue of scans of the thorax and abdominal areas. However, because ofMRI's incredible value as a diagnostic tool for imaging organs and otherbody tissues, many physicians simply take the risk and go ahead andperform MRI on a pacemaker patient. The literature indicates a number ofprecautions that physicians should take in this case, including limitingthe applied power of the MRI in terms of the specific absorptionrate—SAR programming the pacemaker to fixed or asynchronous pacing mode,having emergency personnel and resuscitation equipment standing by(known as “Level II” protocol), and careful reprogramming and evaluationof the pacemaker and patient after the procedure is complete. There havebeen reports of latent problems with cardiac pacemakers after an MRIprocedure occurring many days later (such as increase in or loss ofpacing pulse capture).

There are three types of electromagnetic fields used in an MRI unit. Thefirst type is the main static magnetic field designated B₀ which is usedto align protons in body tissue. The field strength varies from 0.5 to3.0 Tesla in most of the currently available MRI units in clinical use.Some of the newer MRI system fields can go as high as 4 to 6 Tesla. Atthe recent International Society for Magnetic Resonance in Medicine(ISMRM), which was held on 5 and 6 Nov. 2005, it was reported thatcertain research systems are going up as high as 11.7 Tesla and will beready sometime in 2007. A 1.5 T MRI system is over 100,000 times themagnetic field strength of the earth. A static magnetic field of thismagnitude can induce powerful magnetomechanical forces on any magneticmaterials implanted within the patient, including certain componentswithin the cardiac pacemaker and/or lead wire systems themselves. It isunlikely that the static MRI magnetic field can induce currents (dB/dt)into the pacemaker lead wire system and hence into the pacemaker itself.It is a basic principle of physics that a magnetic field must either betime-varying as it cuts across the conductor (dB/dt), or the conductoritself must move within the magnetic field for currents to be induced(dB/dx).

The second type of field produced by magnetic resonance imagingequipment is the pulsed RF field which is generated by the body coil orhead coil, also referred to as B₁. This is used to change the energystate of the protons and illicit MRI signals from tissue. The RF fieldis homogeneous in the central region and has two main components: (1)the magnetic field is circularly polarized in the actual plane; and (2)the electric field is related to the magnetic field by Maxwell'sequations. In general, the RF field is switched on and off duringmeasurements and usually has a frequency of 21 MHz to 64 MHz to 128 MHzdepending upon the static magnetic field strength. The frequency of theRF pulsed varies with the field strength of the main static field, asexpressed in the Lamour Equation:: RF PULSED FREQUENCY (in MHz)=(42.56)(STATIC FIELD STRENGTH (T); where 42.56 MHz per Tesla is the Lamourconstant for H⁺ protons.

The third type of electromagnetic field is the time-varying magneticgradient field designated G_(x,y,z) which is used for spatiallocalization. The gradient field changes its strength along differentorientations and operating frequencies on the order of 1 to 2.2 kHz. Thevectors of the magnetic field gradients in the X, Y and Z directions areproduced by three sets of orthogonally positioned coils and are switchedon only during the measurements. In some cases, the gradient field hasbeen shown to elevate natural heart rhythms (heart beat). This is notcompletely understood, but it is a repeatable phenomenon. There havebeen some reports of gradient field induced ventricular arrhythmiaswhich could be life threatening. However, in contrast, the gradientfield is not considered by some researchers to create any significantadverse effects.

As previously stated, the third type of electromagnetic field is thetime-varying magnetic gradient fields, designated as G_(x), G_(y), andG_(z). The G_(z) gradient is used to distort the B₀ field in the zdirection, thereby creating body ‘slices’ of specific thickness. TheG_(x) and G_(y) fields are used to introduce phase and frequency‘markers’ to specific protons, allowing for an x-y image to begenerated.

The fields operate at roughly 1 to 2.2 kHz, and are generated by threedistinct, orthogonally oriented coils. These fields are only activeduring image generation protocols, and have been shown to have adverseeffects on human physiology. These effects are largely due to theinduced voltages that are generated by the application of a movingmagnetic field on a large area. Following is Faraday's Law of Induction,

${V = {A\;\frac{\mathbb{d}B}{\mathbb{d}t}}},$Where A is the area of the loop, and dB/dt is change in magnetic fluxwith respect to time, it has been shown that the induced voltagesgenerated by the gradient fields, if high enough, can induce peripheralnerve stimulation (PNS). This has been reported in literature as asensation of pain or other discomfort while running relatively high MRIgradients. In more extreme animal testing, cardiac stimulation has beendetected, although this has taken roughly 80 times more energy toachieve than that of PNS. To prevent PNS or cardiac stimulation fromoccurring, industry standards have limited dB/dt to roughly 20 T/sec.

Of interest is the effect of the gradient fields on AIMDs, whichtypically have implanted lead systems. In the case of AIMDs withunipolar lead systems, a circuit loop is formed between the AIMD can,the lead system, the distal TIP, and body tissue (as the return path).An average area created by such a loop is around 225 cm² with the higherlimit about 350 cm². When considering this with the 20 T/sec maximum, itcan be seen that the maximum induced voltage in the loop is 0.700V. Whenone looks at the induced voltage at the pacing tip, it is typically anorder of magnitude lower than the induced voltage in the loop (due torelatively high lead system and device impedances). This is much lowerthan the typical pacing threshold required for an AIMD to stimulateheart tissue.

It is instructive to note how voltages and EMI are induced into animplanted or external lead wire system. At very low frequency (VLF),voltages are induced at the input to the cardiac pacemaker as currentscirculate throughout the patient's body and create differential voltagedrops. In a unipolar system, because of the vector displacement betweenthe pacemaker housing and, for example, the TIP electrode, voltage dropacross body tissues may be sensed due to Ohms Law and the circulating RFsignal. At higher frequencies, the implanted lead wire systems actuallyact as antennas where currents are induced along their length. Theseantennas are not very efficient due to the damping effects of bodytissue; however, this can often be offset by extremely high power fieldsand/or body resonances. At very high frequencies (such as cellulartelephone frequencies), EMI signals are induced only into the first areaof the lead wire system (for example, at the header block of a cardiacpacemaker). This has to do with the wavelength of the signals involvedand where they couple efficiently into the system.

Magnetic field coupling into an implanted lead wire system is based onloop areas. For example, in a cardiac pacemaker, there is a loop formedby the lead wire as it comes from the cardiac pacemaker housing to itsdistal TIP located in the right ventricle. The return path is throughbody fluid and tissue generally straight from the TIP electrode in theright ventricle back up to the pacemaker case or housing. This forms anenclosed area which can be measured from patient X-rays in squarecentimeters. The average loop area is 200 to 225 square centimeters.This is an average and is subject to great statistical variation. Forexample, in a large adult patient with an abdominal implant, theimplanted loop area is much larger (greater than 450 squarecentimeters).

Relating now to the specific case of MRI, the magnetic gradient fieldswould be induced through enclosed loop areas. However, the pulsed RFfields, which are generated by the body coil, would be primarily inducedinto the lead wire system by antenna action.

There are a number of potential problems with MRI, including:

-   -   (1) Closure of the pacemaker reed switch. A pacemaker reed        switch, which can also be a Hall Effect device, is designed to        detect a permanent magnet held close to the patient's chest.        This magnet placement allows a physician or even the patient to        put the implantable medical device into what is known as the        “magnet mode response.” The “magnet mode response” varies from        one manufacturer to another, however, in general, this puts the        pacemaker into a fixed rate or asynchronous pacing mode. This is        normally done for short times and is very useful for diagnostic        purposes. However, when a pacemaker is brought close to the MRI        scanner, the MRI static field can make the pacemaker's internal        reed switch close, which puts the pacemaker into a fixed rate or        asynchronous pacing mode. Worse yet, the reed switch may bounce        or oscillate. Asynchronous pacing may compete with the patient's        underlying cardiac rhythm. This is one reason why pacemaker/ICD        patients have generally been advised not to undergo MRI. Fixed        rate or asynchronous pacing for most patients is not an issue.        However, in patients with unstable conditions, such as        myocardial ischemia, there is a substantial risk for life        threatening ventricular fibrillation during asynchronous pacing.        In most modern pacemakers the magnetic reed switch (or Hall        Effect device) function is programmable. If the magnetic reed        switch response is switched off, then synchronous pacing is        still possible even in strong magnetic fields. The possibility        to open and re-close the reed switch in the main magnetic field        by the gradient field cannot be excluded. However, it is        generally felt that the reed switch will remain closed due to        the powerful static magnetic field. It is theoretically possible        for certain reed switch orientations at the gradient field to be        capable of repeatedly closing and re-opening the reed switch.    -   (2) Reed switch damage. Direct damage to the reed switch is        theoretically possible, but has not been reported in any of the        known literature. In an article written by Roger Christoph        Lüchinger of Zurich, he reports on testing in which reed        switches were exposed to the static magnetic field of MRI        equipment. After extended exposure to these static magnetic        fields, the reed switches functioned normally at close to the        same field strength as before the test.    -   (3) Pacemaker displacement. Some parts of pacemakers, such as        the batteries and reed switch, contain ferrous magnetic        materials and are thus subject to mechanical forces during MRI        (testing is done to ASTM Standards). Pacemaker displacement may        occur in response to magnetic force or magnetic torque (newer        pacemakers and ICDs have less ferrous materials and are less        susceptible to this).    -   (4) Radio frequency field. At the pulsed RF frequencies of        interest in MRI, RF energy can be absorbed and converted to        heat. The power deposited by RF pulses during MRI is complex and        is dependent upon the power, duration and shape of the RF pulse,        the relative long term time averages of the pulses, the        transmitted frequency, the number of RF pulses applied per unit        time, and the type of configuration of the RF transmitter coil        used. Specific absorption rate (SAR) is a measure of how much        energy is induced into body tissues. The amount of heating also        depends upon the volume of the various tissue (i.e. muscle, fat,        etc.) imaged, the electrical resistivity of tissue and the        configuration of the anatomical region imaged. There are also a        number of other variables that depend on the placement in the        human body of the AIMD and its associated lead wire(s). For        example, it will make a difference how much current is induced        into a pacemaker lead wire system as to whether it is a left or        right pectoral implant. In addition, the routing of the lead and        the lead length are also very critical as to the amount of        induced current and heating that would occur. Also, distal TIP        design is very important as the distal TIP itself can act as its        own antenna. Location within the MRI bore is also important        since the electric fields required to generate the RF increase        exponentially as the patient is moved away from MRI bore        center-line (ISO center). The cause of heating in an MRI        environment is two fold: (a) RF field coupling to the lead can        occur which induces significant local heating; and (b) currents        induced during the RF transmission can flow into body tissue and        cause local Ohm's Law heating next to the distal TIP electrode        of the implanted lead. The RF field in an MRI scanner can        produce enough energy to induce lead wire currents sufficient to        destroy some of the adjacent myocardial tissue. Tissue ablation        has also been observed. The effects of this heating are not        readily detectable by monitoring during the MRI. Indications        that heating has occurred would include an increase in pacing        threshold, venous ablation, Larynx ablation, myocardial        perforation and lead penetration, or even arrhythmias caused by        scar tissue. Such long term heating effects of MRI have not been        well studied yet.    -   (5) Alterations of pacing rate due to the applied radio        frequency field. It has been observed that the RF field may        induce undesirable fast cardiac pacing (QRS complex) rates.        There are various mechanisms which have been proposed to explain        rapid pacing: direct tissue stimulation, interference with        pacemaker electronics or pacemaker reprogramming (or reset). In        all of these cases, it would be desirable to raise the lead        system impedance (to reduce RF current), make the feedthrough        capacitor more effective and provide a very high degree of        protection to AIMD electronics. This will make alterations in        pacemaker pacing rate and/or pacemaker reprogramming much more        unlikely.    -   (6) Time-varying magnetic gradient fields. The contribution of        the time-varying gradient to the total strength of the MRI        magnetic field is negligible, however, pacemaker systems could        be affected because these fields are rapidly applied and        removed. The time rate of change of the magnetic field is        directly related to how much electromagnetic force (EMF) and        hence current can be induced into a lead wire system. Lüchinger        reports that even using today's gradient systems with a        time-varying field up to 60 Tesla per second, the induced        currents are likely to stay below the biological thresholds for        cardiac fibrillation. A theoretical upper limit for the induced        voltage by the time-varying magnetic gradient field is 20 volts.        Such a voltage during more than 0.1 milliseconds could be enough        energy to directly pace the heart.    -   (7) Heating. Currents induced by time-varying magnetic gradient        fields may lead to local heating. Researchers feel that the        calculated heating effect of the gradient field is much less as        compared to that caused by the RF field and therefore may be        neglected.

There are additional problems possible with implantable cardioverterdefibrillators (ICDs). ICDs use different and larger batteries whichcould cause higher magnetic forces. The programmable sensitivity in ICDsis normally much higher than it is for pacemakers, therefore, ICDs mayfalsely detect a ventricular tacchyarrhythmia and inappropriatelydeliver therapy. In this case, therapy might include anti-tacchycardiapacing, cardio version or defibrillation (high voltage shock) therapies.MRI magnetic fields may prevent detection of a dangerous ventriculararrhythmia or fibrillation. There can also be heating problems of ICDleads which are expected to be comparable to those of pacemaker leads.Ablation of vascular walls is another concern. There have also beenreports of older model ICDs being severely effected by the MRI pulsed RFfield. In these cases, there have been multiple microprocessor resetsand even cases of permanent damage where the ICD failed to functionafter the MRI procedure. In addition, ICDs have exhibited a differenttype of problem when exposed to MRI fields. That is, during an MRIexposure, the ICD might inappropriately sense the MRI RF-field orgradient fields as a dangerous ventricular arrhythmia. In this case, theICD will attempt to charge its high energy storage capacitor and delivera high voltage shock to the heart. However, within this chargingcircuit, there is a transformer that is necessary to function in orderto fully charge up the high energy storage capacitor. In the presence ofthe main static field (B₀) field, the ferrite core of this transformertends to saturate thereby reducing its efficiency. This means the highenergy storage capacitor cannot fully charge. Reports of repeated lowvoltage shocks are in the literature. These repeated shocks and thisinefficient attempt to charge the battery can cause premature batterydepletion of the ICD. Shortening of battery life is of course, a highlyundesirable condition.

In summary, there are a number of studies that have shown that MRIpatients with active implantable medical devices, such as cardiacpacemakers, can be at risk for potential hazardous effects. However,there are a number of anecdotal reports that MRI can be safe forextremity imaging of pacemaker patients (i.e. the AIMD is outside thebore). These anecdotal reports are of interest; however, they arecertainly not scientifically convincing that all MRI can be safe. Aspreviously mentioned, just variations in the pacemaker lead wire lengthcan significantly effect how much heat is generated. From the layman'spoint of view, this can be easily explained by observing the typicallength of the antenna on a cellular telephone compared to the verticalrod antenna more common on older automobiles. The relatively shortantenna on the cell phone is designed to efficiently couple with thevery high frequency wavelengths (approximately 950 MHz) of cellulartelephone signals. In a typical AM and FM radio in an automobile, thesewavelength signals would not efficiently couple to the relatively shortantenna of a cell phone. This is why the antenna on the automobile isrelatively longer. An analogous situation exists on the MRI system. Ifone assumes, for example, a 3.0 Tesla MRI system, which would have an RFpulsed frequency of 128 MHz, there are certain exact implanted leadlengths that would couple efficiently as fractions of the 128 MHzwavelength. Ignoring the effects of body tissue, as an example, thebasic wavelength equation in meters is 300 divided by the frequency inMHz. Accordingly, for a 3.0 Tesla MRI system, the wavelength is 2.34meters or 234 centimeters. An exact ¼ wavelength antenna then would be ¼of this which is 58.59 centimeters. This falls right into the range forthe length of certain pacemaker lead wire implants. It is typical that ahospital will maintain an inventory of various leads and that theimplanting physician will make a selection depending on the size of thepatient, implant location and other factors. Accordingly, the implantedor effective lead wire length can vary considerably. Another variablehas to do with excess lead wire. It is typical that the physician, afterdoing a pacemaker lead wire insertion, will wrap up any excess lead wirein the pectoral pocket. This can form one, two or even three turns ofexcess lead. This forms a loop in that specific area, however, theresulting longer length of wire that goes down into the right ventricle,is what would then couple efficiently with the MRI RF pulsed frequency.As one can see, the amount of unwound up lead length is considerablyvariable depending upon patient geometry. There are certain implantedlead wire lengths that just do not couple efficiently with the MRIfrequency and there are others that would couple very efficiently andthereby produce the worst case for heating. The actual situation for animplanted lead wire is far more complex due to the varying permittivityand dielectric properties of body tissues and the accompanying shifts inwavelengths.

The effect of an MRI system on the function of pacemakers, ICDs andneurostimulators depends on various factors, including the strength ofthe static magnetic field, the pulse sequence (gradient and RF fieldused), the anatomic region being imaged, and many other factors. Furthercomplicating this is the fact that each manufacturer's pacemaker and ICDdesigns behave differently. Most experts still conclude that MRI for thepacemaker patient should not be considered safe. Paradoxically, thisalso does not mean that the patient should not receive MRI. Thephysician must make an evaluation given the pacemaker patient'scondition and weigh the potential risks of MRI against the benefits ofthis powerful diagnostic tool. As MRI technology progresses, includinghigher field gradient changes over time applied to thinner tissue slicesat more rapid imagery, the situation will continue to evolve and becomemore complex. An example of this paradox is a pacemaker patient who issuspected to have a cancer of the lung. RF ablation treatment of such atumor may require stereotactic imaging only made possible through realtime fine focus MRI. With the patient's life literally at risk, and withinformed patient consent, the physician may make the decision to performMRI in spite of all of the previously described attendant risks to thepacemaker system.

Insulin drug pump systems do not seem to be of a major current concerndue to the fact that they have no significant antenna components (suchas implanted lead wires). However, implantable pumps presently work onmagneto-peristaltic systems, and must be deactivated prior to MRI. Thereare newer (unreleased) systems that would be based on solenoid systemswhich will have similar problems.

It is clear that MRI will continue to be used in patients with an activeimplantable medical device. There are a number of other hospitalprocedures, including electrocautery surgery, lithotripsy, etc., towhich a pacemaker patient may also be exposed. Accordingly, there is aneed for circuit protection devices which will improve the immunity ofactive implantable medical device systems to diagnostic procedures suchas MRI.

As one can see, many of the undesirable effects in an implanted leadwire system from MRI and other medical diagnostic procedures are relatedto undesirable induced currents in the lead wire system. This can leadto overheating either in the lead wire or at the tissue interface at thedistal TIP. At the 2006 SMIT Conference, the FDA reported on aneurostimulator patient whose implanted leads were sufficiently heatedthat severe burns occurred resulting in the need for multipleamputations. In pacemaker patients, these currents can also directlystimulate the heart into sometimes dangerous arrhythmias. The abovedescriptions of problems that a pacemaker, ICD or neurostimulatorpatients may encounter during MRI or similar medical diagnosticprocedures are only examples of a general need. A patient wearingexternal devices, such as an external drug pump, an externalneurostimulator, EKG leads, (skin patches) or ventricular assistdevices, may also encounter problems during an MRI procedure. All of theabove descriptions regarding overheating of lead wires, overheating ofdistal tips or electromagnetic interference are all concerns. The novelresonant TANK filter of the present invention is equally applicable toall of these other devices. It is also applicable to probes andcatheters that are used during certain real time medical imagingprocedures such as MRI. The present invention is applicable to a widerange of both implanted and external medical device systems. In general,the present invention is a circuit protection device that protects apatient undergoing high RF power medical diagnostic procedures.

Accordingly, there is a need for a novel resonant EMI TANK filterassembly which can be placed at various locations along the medicaldevice lead wire system, which also prevents current from circulating atselected frequencies of the medical therapeutic device. Preferably, suchnovel TANK filters would be designed to resonate at or near 64 MHz foruse in an MRI system operating at 1.5 Tesla (or 128 MHz for a 3 Teslasystem), and have broad application to other fields, includingtelecommunications, military, space and the like. The present inventionfulfills these needs and provides other related advantages.

SUMMARY OF THE INVENTION

The present invention consists of novel resonant TANK filters to beplaced at the distal TIP and/or at various locations along the medicaldevice lead wires or circuits. These TANK filters inhibit or preventcurrent from circulating at selected frequencies of the medicaltherapeutic device. For example, for an MRI system operating at 1.5Tesla, the pulse RF frequency is 64 MHz, as described by the LamourEquation. The novel TANK filter of the present invention can be designedto resonate at or near 64 MHz and thus create a high impedance (ideallyan open circuit) in the lead wire system at that selected frequency. Forexample, the novel TANK filter of the present invention, when placed atthe distal TIP of a pacemaker lead wire, will significantly reduce RFcurrents from flowing through the distal TIP and into body tissue. Thenovel TANK filter also reduces EMI from flowing in the lead wires of apacemaker, for example, thereby providing added protection to sensitiveelectronic circuits. It will be obvious to those skilled in the art thatall of the embodiments described herein are equally applicable to a widerange of other implantable and external medical devices, including deepbrain stimulators, spinal cord stimulators, drug pumps, probes,catheters and the like. The present invention fulfills all of the needsregarding reduction or elimination of undesirable currents andassociated heating in medical devices and/or their associated lead wiresystems. The novel TANK filter structures as described herein also havea broad application to other disciplines, including telecommunications,military, space and the like.

Electrically engineering a capacitor in parallel with an inductor isknown as a TANK filter. It is also well known that when a near-idealTANK filter is at its resonant frequency, it will present a very highimpedance. Since MRI equipment produces very large RF pulsed fieldsoperating at discrete frequencies, this is an ideal situation for aspecific resonant TANK filter. TANK filters are more efficient foreliminating one single frequency than broadband filters. Because theTANK filter is targeted at this one frequency, it can be much smallerand volumetrically efficient. In addition, the way MRI couples with leadwire systems, various loops and associated currents are generated. Forexample, at the distal TIP of a cardiac pacemaker, directelectromagnetic forces (EMFs) can be produced which result in currentloops through the distal TIP and into the associated myocardial tissue.This current system is largely decoupled from the currents that areinduced near the active implantable medical device, for example, nearthe cardiac pacemaker. There the MRI may set up a separate loop with itsassociated currents. Accordingly, one or more TANK filters may berequired to completely control all of the various induced EMI andassociated currents in a lead wire system.

A major challenge for designing a TANK filter for human implant is thatit must be very small in size, biocompatible, and highly reliable.Coaxial geometry is preferred. The reason that coaxial is preferred isthat lead wires are placed at locations in the human body primarily byone of two main methods. These include guide wire lead insertion. Forexample, in a cardiac pacemaker application, a pectoral pocket iscreated. Then, the physician makes a small incision between the ribs andaccesses the subclavian vein. The pacemaker lead wires are stylusguided/routed down through this venous system through the aortic arch,through the right atrium, through the tricuspid valve and into, forexample, the right ventricle. Another primary method of installing leadwires (particularly for neurostimulators) in the human body is bytunneling. In tunneling, a surgeon uses special tools to tunnel underthe skin and through the muscle, for example, up through the neck toaccess the Vagus nerve or the deep brain. In both techniques, it is veryimportant that the lead wires and their associated electrodes at thedistal TIPs be very small. The present invention solves these issues byusing very novel miniature coaxial or rectilinear capacitors that havebeen adapted with an inductance element to provide a parallel TANKcircuit. Prior art capacitors are well known and consist of ceramicdiscoidal feedthrough capacitors and also single layer and multilayertubular capacitors and multilayer rectangular capacitors, and thick-filmdeposited capacitors. The present invention shows design methodologiesto adapt all of these previous tubular, feedthrough or rectangulartechnologies to incorporate a parallel inductor in novel ways. It willbe obvious to those skilled in the art that a number of other capacitortechnologies can be adapted to the present invention. This includes filmcapacitors, glass capacitors, tantalum capacitors, electrolyticcapacitors, stacked film capacitors and the like.

As previously mentioned, the value of the capacitance and the associatedparallel inductor can be adjusted to achieve a specific resonantfrequency (SRF). The novel TANK filters described herein can be adaptedto a number of locations within the overall implantable medical devicesystem. That is, the novel TANK filter can be incorporated at or nearany part of the medical device lead wire system or the distal TIP. Inaddition, the novel TANK filter can be placed anywhere along the leadwire system. In another embodiment, the TANK filter can actually beplaced inside the active implantable medical device.

The present invention which resides in novel coaxial or rectilinear TANKfilters is also designed to work in concert with the EMI filter which istypically used at the point of lead wire ingress and egress of theactive implantable medical device. For example, see U.S. Pat. No.6,999,818 filed Apr. 15, 2004, entitled INDUCTOR CAPACITOR EMI FILTERFOR HUMAN IMPLANT APPLICATIONS; U.S. patent application Ser. No.11/097,999 filed Mar. 31, 2005, entitled APPARATUS AND PROCESS FORREDUCING THE SUSCEPTIBILITY OF ACTIVE IMPLANTABLE MEDICAL DEVICES TOMEDICAL PROCEDURES SUCH AS MAGNETIC RESONANCE IMAGING; U.S. patentapplication Ser. No. 11/163,915 filed Nov. 3, 2005, entitled PROCESS FORTUNING AN EMI FILTER TO REDUCE THE AMOUNT OF HEAT GENERATED IN IMPLANTEDLEAD WIRES DURING MEDICAL PROCEDURES SUCH AS MAGNETIC RESONANCE IMAGING;and U.S. Patent Application No. 60/767,484 filed Apr. 3, 2006, entitledLOW LOSS BAND PASS FILTER FOR RF DISTANCE TELEMETRY PIN ANTENNAS OFACTIVE IMPANTABLE MEDICAL DEVICES; the contents of all beingincorporated herein by reference. All four of these documents describenovel inductor capacitor combinations for low pass EMI filter circuits.It is of particular interest that by increasing the number of circuitelements of the passive low pass filter at the AIMD hermeticfeedthrough, one can reduce the overall capacitance value of said filterwhich primarily defines the input impedance of the AIMD. It is importantto reduce the capacitance value to raise the input impedance of theAIMD. Increasing the input impedance of the AIMD will reduce the amountof current that would flow in lead wire systems at high frequencies suchas those associated with the RF pulsed frequencies of MRI equipment.Accordingly, it is a feature of the present invention that the novelTANK filters are designed to be used in concert with prior art low passfilters.

The present invention is also applicable to probes and catheters. Forexample, ablation probes are used to selectively cauterize or burntissue on the outside or inside of the heart to control erratic pulsesfrom the sinus node or the outside of the A-V node. These procedures arebest performed during real time MRI imaging. However, a major concern isthe overheating of the distal TIP at inappropriate times because of theinduced currents from the MRI system. It will be obvious to one skilledin the art that the novel TANK filters of the present invention can beadapted to any probe, TIP or catheter that is used in or on the humanbody.

Other features and advantages of the present invention will becomeapparent from the following more detailed description, taken inconjunction with the accompanying drawings which illustrate, by way ofexample, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate the invention. In such drawings:

FIG. 1 is a wire-formed diagram of a generic human body showing a numberof active medical devices (AMDs) and associated internal and externallead wires;

FIG. 2 is a perspective and somewhat schematic view of a prior artactive implantable medical device (AIMD) including a lead wire directedto the heart of a patient;

FIG. 3 is an enlarged sectional view taken generally along the line 3-3of FIG. 2;

FIG. 4 is a view taken generally along the line 4-4 of FIG. 3;

FIG. 5 is a perspective/isometric view of a prior art rectangularquadpolar feedthrough capacitor of the type shown in FIGS. 3 and 4;

FIG. 6 is a sectional view taken generally along the line 6-6 of FIG. 5;

FIG. 7 is a sectional view taken generally along the line 7-7 of FIG. 5;

FIG. 8 is a diagram of a unipolar active implantable medical device;

FIG. 9 is a diagram similar to FIG. 8, illustrating a bipolar AIMDsystem;

FIG. 10 is a diagram similar to FIGS. 8 and 9, illustrating a bipolarlead wire system with a distal TIP and RING, typically used in a cardiacpacemaker;

FIG. 11 is a schematic diagram showing a parallel combination of aninductor L and a capacitor C forming the TANK filter of the presentinvention placed in the lead wire systems of FIGS. 8-10;

FIG. 12 is a chart illustrating calculation of frequency of resonancefor the parallel TANK of FIG. 11;

FIG. 13 is a graph showing impedance versus frequency for the idealparallel TANK circuit of FIG. 11;

FIG. 14 is an equation for the impedance Z_(ab) of an inductor inparallel with a capacitor;

FIG. 15 is a chart illustrating impedance equations for the inductivereactance (X_(L)) and the capacitive reactance (X_(C)) of the parallelTANK circuit in FIG. 11;

FIG. 16 is a schematic diagram illustrating the parallel TANK circuit ofFIG. 11, except in this case the inductor and the capacitor haveparasitic or deliberate resistive losses and are not ideal;

FIG. 17 is a diagram similar to FIG. 8, illustrating the TANK filtercircuit added near a distal electrode of an AIMD;

FIG. 18 is a schematic representation of the ideal TANK filter of thepresent invention, using switches to illustrate its function;

FIG. 19 is a schematic diagram similar to FIG. 18, illustrating the lowfrequency model of the TANK filter;

FIG. 20 is a schematic diagram similar to FIGS. 18 and 19, illustratingthe model of an ideal TANK filter of the present invention at itsresonant frequency;

FIG. 21 is a schematic diagram similar to FIGS. 18-20, illustrating amodel of the TANK filter at high frequencies (well above resonance);

FIG. 22 is a diagram similar to FIG. 9, redrawn to show multiple TANKfilters in multiple electrodes;

FIG. 23 is a decision tree block diagram illustrating a process fordesigning the TANK filters of the present invention;

FIG. 24 is a graph of insertion loss verses frequency for TANK filtershaving differing quality “Q” factors;

FIG. 25 is a tracing of an exemplary patient x-ray showing an implantedcardiac pacemaker and cardioverter defibrillator and corresponding wiresystem;

FIG. 26 is a line drawing of an exemplary patient cardiac x-ray of abi-ventricular lead wire system;

FIG. 27 illustrates a bipolar cardiac pacemaker lead wire showing thedistal TIP and the distal RING electrodes;

FIG. 28 is an enlarged, fragmented schematic illustration of the areaillustrated by the line 28-28 in FIG. 27 with the L-C TANK of thepresent invention shown in series with both the distal TIP and the RINGelectrodes;

FIG. 29 is a perspective view of a prior art tubular feedthroughcapacitor;

FIG. 30 is a sectional view taken along the line 30-30 of FIG. 29;

FIG. 31 is a sectional view similar to that shown in FIG. 30,illustrating a prior art multilayer tubular capacitor;

FIG. 32 is a perspective view similar to FIG. 29, illustrating amodification including the distal TIP electrode in accordance with thepresent invention of the tubular feedthrough capacitor of the tankfilter;

FIG. 33 is an inverted perspective view of a high surface area distalTIP illustrated in FIG. 32;

FIG. 34 illustrates an active fixation helix TIP alternative to theinverted distal TIP shown in FIG. 33;

FIG. 35 is a sectional view taken along the line 35-35 of FIG. 32;

FIG. 36 is an electrical schematic diagram for the ideal TANK filter ofFIGS. 32 and 35;

FIG. 37 is a cross-sectional diagram similar to FIG. 35, illustratingthe present invention applied to the multilayer capacitor shown in FIG.31;

FIG. 38 is an electrical schematic similar to FIG. 36;

FIG. 39 is a partially fragmented perspective view of a prior artunipolar discoidal feedthrough capacitor;

FIG. 40 is a fragmented sectional view of the feedthrough capacitor ofFIG. 39 mounted to a ferrule and hermetic terminal of an AIMD;

FIG. 41 is an electrical schematic diagram of the feedthrough capacitorof FIGS. 39 and 40;

FIG. 42 is a sectional and diagrammatic view of a novel adaptation ofthe prior art feedthrough capacitor shown in FIGS. 39 and 40, adapted inaccordance with the present invention;

FIG. 43 is an electrical schematic diagram illustrating the electricalcharacteristics of the structure shown in FIG. 42;

FIG. 44 is a sectional view similar to FIG. 42 illustrating the novelstructure placed at the terminus of a distal TIP;

FIG. 45 is an electrical schematic diagram of the structure shown inFIG. 44;

FIG. 46 is a diagram showing another arrangement wherein the novel TANKcircuits described herein can be placed inside the hermetically sealedhousing of an AIMD;

FIG. 47 is an external view of a novel active implantable medical devicethat may or not have lead wires, known as a Bion;

FIG. 48 is a sectional view similar to FIG. 47, wherein a TANK filter ofthe present invention is placed inside at the cap electrode;

FIG. 49 is a sectional view similar to FIGS. 47 and 48, illustrating analternative inline Bion, wherein a TANK filter of the present inventionis disposed at each end;

FIG. 50 is an electrical schematic diagram illustrating utilization ofthe TANK filter circuits of the present invention in a multiple resonantfrequency series configuration;

FIG. 51 is an isometric view of a prior art air-wound inductor;

FIG. 52 is an enlarged fragmented perspective view taken along the area52-52 in FIG. 51;

FIG. 53 is a perspective view of a prior art hollow ferrite core whichhas high permeability;

FIG. 54 is a view similar to FIG. 53, illustrating an optional prior artsolid ferrite or powdered iron core;

FIG. 55 is a perspective view illustrating a prior art wire wound aroundthe high permeability ferrite core shown in FIG. 53;

FIG. 56 is a perspective view of the ferrite core of FIG. 53 withmultiple turns of wire placed thereon;

FIG. 57 is a cross-sectional view taken generally along the line 57-57of FIG. 56;

FIG. 58 is a perspective view of a novel non-ferrite chip inductor thatmay be utilized to build a TANK in place of the spiral wound inductorsshown above;

FIG. 59 is an enlarged fragmented view taken generally of the areadesignated by 59-59 in FIG. 58, and showing an alternativeconfiguration;

FIG. 60 is the inductor meander substrate of FIG. 59 with a small gapadded to facilitate electrical testing of the capacitor element of thetank by itself.

FIG. 61 is the schematic diagram taken from FIG. 60.

FIG. 62 illustrates electrically closing the gap of FIG. 60 with a smallamount of conductive material.

FIG. 63 is an exploded perspective view illustrating an hermeticallysealed assembly of the novel distal TIP TANK filter of the presentinvention;

FIG. 64 is a sectional view illustrating the assembly of the bottomthree components illustrated in FIG. 63;

FIG. 65 is a sectional view illustrating assembly of all of thecomponents of FIG. 63;

FIG. 66 is an electrical schematic diagram relating to the assembly ofFIG. 65;

FIG. 67 is an enlarged fragmented sectional view taken of the areaindicated by the line 67-67 in FIG. 65;

FIG. 68 is a perspective and somewhat schematic illustration of aninductive element which is completely imbedded within a novel tubularceramic capacitor structure;

FIG. 69 is a schematic cross-sectional view taken generally along theline 69-69 of FIG. 68, illustrating the manner in which the inductor isimbedded within the capacitor dielectric material;

FIG. 70 is an enlarged sectional view taken generally along the line69-69 of FIG. 68, of a multilayer tubular capacitor with an embeddedinductor element;

FIG. 71 is an electrical schematic diagram illustrating the TANK filterof FIGS. 68-70;

FIG. 72 is a sectional view similar to FIG. 70, illustrating analternative arrangement of capacitive and inductive elements;

FIG. 73 is another sectional view similar to FIGS. 70 and 72illustrating yet another alternative construction of the TANK filter ofthe present invention;

FIG. 74 is a sectional view taken generally along the line 74-74 of FIG.73;

FIG. 75 is a sectional view taken generally along the line 75-75 of FIG.72;

FIG. 76 is a sectional view similar to FIGS. 74 and 75, illustratinganother possible arrangement of a number of parallel inductor spiralswithin the tubular capacitor;

FIG. 77 is an equation for inductors in parallel;

FIG. 78 is a perspective view of a prior art rectangular monolithicceramic capacitor (MLCC);

FIG. 79 is a sectional view taken generally along the line 79-79 of FIG.78;

FIG. 80 is a perspective/isometric view of a novel composite monolithicceramic capacitor-parallel resonant TANK (MLCC-T) which forms a TANKfilter in accordance with the present invention;

FIG. 81 is an exploded view of the various layers of the MLCC-T TANKfilter of FIG. 80;

FIG. 82 is an electrical schematic diagram of the MLCC-T TANK filter ofFIGS. 80 and 81;

FIG. 83 illustrates various inductor meander shapes which may beembedded into the MLCC-T of FIGS. 80 and 81;

FIG. 84 is a chart showing the total inductance equation for threeparallel inductors;

FIG. 85 is a perspective view of the prior art MLCC of FIG. 78 showingan exemplary inductor circuit trace applied to an upper surface thereof;

FIG. 86 is a schematic diagram of the MLCC-T of FIG. 85;

FIG. 87 is an exploded perspective view of a novel MLCC-T similar tothat shown in FIG. 85, illustrating another way to deposit any of theinductor tracing shapes illustrated in FIG. 83;

FIG. 88 is the actual (non-ideal) electrical schematic diagram (model)of the structure of FIGS. 80, 85 and 87;

FIG. 89 is a sectional view taken along the line 89-89 of FIG. 87;

FIG. 90 is a sectional view similar to FIG. 89, illustrating analternative configuration wherein two inductor layers are deposited onopposite sides of a substrate;

FIG. 91 is a sectional view similar to FIGS. 89 and 90, illustrating amulti-layer substrate having an embedded inductor layer along withsurface inductor layers;

FIG. 92 is a sectional view similar to FIGS. 89-91, illustrating acompletely embedded multi-layer substrate where there are no inductorson the surface;

FIG. 93 is a schematic view similar to FIG. 28, illustrating a bipolarpacemaker lead wire system;

FIG. 94 is an enlarged view of the area taken generally along line 94-94in FIG. 93;

FIG. 95 is an electrical schematic representation of the coiled inductorwrapped about the prior art MLCC shown in FIGS. 93 and 94;

FIG. 96 is a more detailed electrical schematic illustration of theparallel TANK circuit of the present invention;

FIG. 97 is an electrical schematic showing a very low frequency(biological) model of the TANK filter circuit of FIG. 96;

FIG. 98 is an equivalent circuit model for the TANK filter circuit ofFIG. 96 at very high frequencies that are well above the resonantfrequency;

FIG. 99 is a perspective view of one geometry for a prior art MLCCcapacitor wherein the length to width ratio forms a capacitor that willinherently have very low equivalent series resistance (ESR);

FIG. 100 is a perspective view of a first electrode plate set of theMLCC of FIG. 99;

FIG. 101 is a perspective view of another electrode plate set of theMLCC of FIG. 99;

FIG. 102 is a perspective view of an alternative geometric embodimentfor the prior art MLCC capacitor in comparison with that shown in FIG.99, wherein the width to length ratios have been reversed and the ESRwill be relatively increased;

FIG. 103 is a perspective view of a first electrode plate set embeddedin the MLCC capacitor of FIG. 102;

FIG. 104 is perspective view of a second electrode plate set embeddedwithin the MLCC capacitor of FIG. 102;

FIG. 105 is an enlarged fragmented view of the area taken along line 105of FIG. 103, illustrating a novel method whereby one can increase theequivalent series resistance of the capacitor electrodes by includingholes or apertures within the deposited electrodes;

FIG. 106 is a view similar to FIG. 105 wherein the holes in theelectrode plate have varying diameters;

FIG. 107 is a perspective view of MLCC-T TANK filter utilizing custom orcommercially available inductor chips;

FIG. 108 is a perspective view of a first set of electrode platesembedded within the capacitor of the structure shown in FIG. 107;

FIG. 109 is a perspective view of a second set of electrode platesembedded within the capacitor of the MLCC-T structure shown in FIG. 107;

FIG. 110 is an electrical schematic diagram for the MLCC-T structure ofFIG. 107;

FIG. 111 is a perspective view of an alternative embodiment MLCC-Twherein a single inductor chip is placed across a specially formed MLCCchip capacitor;

FIG. 112 is a perspective view of a first set of electrode platesforming the capacitor of the structure in FIG. 111;

FIG. 113 is a perspective view of a second set of electrode platesincorporated into the capacitor of the MLCC-T structure shown in FIG.111;

FIG. 114 is an electrical schematic diagram for the MLCC-T structure ofFIG. 111;

FIG. 115 is a perspective view of a prior art unipolar coaxial capacitorwith a parallel inductor spiral deposited on an upper surface thereof;

FIG. 116 is the electrical schematic diagram of the TANK filterillustrated in FIG. 115;

FIG. 117 is a sectional view taken generally along the line 117-117 ofFIG. 115;

FIG. 118 is a perspective view similar to FIG. 115, wherein thefeedthrough capacitor and inductor are square rather than circular;

FIG. 119 illustrates a method of using an abrasive microblaster or lasertrimmer to erode electrode plates in order to tune the resonantfrequency of the tank;

FIG. 120 illustrates eroding away a portion of one of the electrode setsfrom the capacitor of FIG. 119 taken generally along the line of120-120;

FIG. 121 illustrates eroding one of the opposite electrode plate setstaken from FIG. 119 taken generally along the line of 121-121;

FIG. 122 is a methodology of trimming any of the inductors of the tankof the present invention, by adding an electrical conductive material toshort adjacent turns;

FIG. 123 is an alternate methodology of actually tuning the inductor byincreasing its inductor value, by removing short circuits across turnsby laser trimming and the like;

FIG. 124 is a close up view taken generally from the area 124-124 fromFIG. 123, illustrating laser ablation to open up turns of the inductor;

FIG. 125 is a sectional view of a novel hermetically sealed unipolarfeedthrough capacitor-inductor TANK filter embodying the presentinvention;

FIG. 126 is a sectional view similar to FIG. 125, illustrating analternative embodiment for a hermetically sealed TANK filter assembly;

FIG. 127 is an electrical schematic illustration for the TANK filter ofFIGS. 125 and 126;

FIG. 128 is a sectional and partially exploded view of yet anotherhermetically sealed package containing the novel inductor-capacitorMLCC-T embodying the present invention;

FIG. 129 is a perspective view of a distal electrode pad applicable to awide variety of neurostimulator applications;

FIG. 130 is a sectional view taken generally along the line 130-130 ofFIG. 129;

FIG. 131 is an exploded perspective view of an alternative structureaccomplishing the same filtering result as the structure shown in FIGS.129 and 130;

FIG. 132 is a vertical sectional view of the components illustrated inFIG. 131, in their assembled configuration;

FIG. 133 is a sectional view similar to FIG. 132, illustrating anotheralternative for building up the novel parallel inductor TANK filter forneurostimulator applications;

FIG. 134 is an exploded perspective view of the components of thestructure shown in FIG. 133;

FIG. 135 is a table illustrating various fabrication methods formanufacturing a thick film TANK circuit;

FIG. 136 is a perspective view of an alternative rectilinearconstruction for a thick film deposited TANK filter embodying thepresent invention;

FIG. 137 is an electrical schematic diagram of a neurostimulatorelectrodes shown in FIGS. 130, 132, 133 and 136;

FIG. 138 is an exploded view of the neurostimulator electrode of FIG.136, showing how the various layers of the novel distal TIP TANK circuitare laid down;

FIG. 139 is a perspective view of the novel inductor TANK filter shownin FIG. 136, which has been hermetically sealed by a glass seal orbiocompatible polymer overlay;

FIG. 140 is a perspective representation illustrating how a glass sealor biocompatible polymer similar to that shown in FIG. 139 may be usedto hermetically seal other types of TANK filters of the presentinvention;

FIG. 141 is an exploded perspective view of a prior art feedthroughcapacitor and a co-bonded inductor spiral substrate which is adhered tothe capacitor;

FIG. 142 is a perspective view of a composite unipolar MLCC-Tfeedthrough in accordance with the present invention;

FIG. 143 is an exploded perspective view of the various layerscomprising the MLCC-T of FIG. 142;

FIG. 144 is a sectional view taken generally along the line 144-144 ofFIG. 142;

FIG. 145 is a sectional view of a prior art active fixation distal TIP;

FIG. 146 is taken along the line 146-146 from FIG. 145 incorporating thetank circuit of the present invention;

FIG. 147 is a cross-section of an active fixation TIP similar to FIG.145 except that a tank filter of the present invention has been addedinside;

FIG. 148 is a cross-section taken generally from line 148-148 from FIG.147 illustrating the tank filter of the present invention inside anactive fixation distal TIP;

FIG. 149 is taken generally from section 149-149 from FIG. 148 andillustrates a novel series inductor which is highly volumetricallyefficient;

FIG. 149A is an isometric view of the complete structure shown in FIG.149;

FIG. 150 is the schematic diagram for the inductor of FIGS. 149 and149A;

FIG. 151 is an exploded assembly view illustrating an alternativeembodiment of the inductor capacitor tank previously illustrated in FIG.148;

FIG. 151A is an isometric view of the completed structure shown in FIG.151;

FIG. 152 is the schematic diagram of the novel tank filter chippreviously illustrated in FIGS. 151 and 151A;

FIG. 153 illustrates the impedance vs. frequency curves for the noveltank filter previously illustrated in FIGS. 151 and 151A;

FIG. 154 is an isometric view of a novel composite tank filter of thepresent invention which could also be placed into the active fixationTIP previously illustrated in FIGS. 147 and 148;

FIG. 155 is the schematic diagram of the novel tank filter previouslyillustrated in FIG. 154;

FIG. 156 is an exploded view of the internal layers of the novel tankshown in FIG. 154;

FIG. 157 is an exploded view of an alternative embodiment of the novelMLCC tank previously illustrated in FIGS. 154 and 156;

FIG. 157A is an isometric view showing the completed tank filter fromFIG. 157;

FIG. 158 is a sectional view of an active fixation distal TIP embodyingthe novel tank filters previously illustrated in FIGS. 154 and 157A;

FIG. 159 is a sectional view of an active fixation TIP employing tubularcapacitor tank filters of the present invention;

FIG. 160 is a fragmented sectional view of a prior art neurostimulationelectrode probe;

FIG. 161 is an enlarged sectional view of the area 161 in FIG. 160,illustrating modifications to the prior art structure to incorporate thenovel MLCC-T TANK filter of the present invention;

FIG. 162 is a view similar to FIG. 2, but illustrating how the TANKfilters of the present invention may be incorporated at the point oflead wire ingress and at other strategic locations inside the circuitryof the active implantable medical device;

FIG. 163 is a fragmented sectional view of the prior art broadband lowpass feedthrough capacitor of FIG. 3, illustrating how an MLCC-T inaccordance with the present invention is incorporated therein;

FIG. 164 is a sectional view illustrating an alternative method forinstalling MLCC-T TANK filters in series with a prior art broadbandfeedthrough capacitor;

FIG. 165 illustrates how tank filters that have been previouslydescribed in FIGS. 35, 37, 42, and 68-76 could all be used incombination with a prior art feedthrough capacitor;

FIG. 166 is an electrical schematic illustration for the MLCC-T TANKfilters shown in FIGS. 163, 164 and 165;

FIG. 167 is an isometric view of a typical electrocardiogram (EKG/ECG)skin patch and lead wire that can be placed on a patient's chest, legsor other parts of the body to enable cardiac monitoring, oralternatively an EEG lead wire and patch that would be placed on thehead.

FIG. 168 illustrates the schematic of TANK filter of the presentinvention placed either at or near the skin electrode patch of FIG. 167;and

FIG. 169 illustrates the overall system of an implantable medical devicesuch as a cardiac pacemaker illustrating the role of the prior artfeedthrough capacitor technology in conjunction with the TANK shown at adistal TIP.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in the drawings, for purposes of illustration, the presentinvention resides in the placement of TANK filters in series with leadwires or circuits of active medical devices to protect the patientand/or medical device from undesirable electromagnetic interferencesignals, such as those generated during MRI and other medicalprocedures. The present invention also resides in the design,manufacturing, and tuning of such TANK filters to be used in the leadwires or active medical devices. As will be explained more fully herein,the invention is applicable to a wide range of external medical devices,probes, catheters, monitoring lead wires and the like that may betemporarily inserted onto a patient or that a patient may be wearing orconnected to during medical diagnostic procedures, such as MRI.

In the following description, functionally equivalent elements shown invarious embodiments will often be referred to utilizing the samereference number.

FIG. 1 illustrates various types of active implantable and externalmedical devices 100 that are currently in use. FIG. 1 is a wire formeddiagram of a generic human body showing a number of implanted medicaldevices. 100A represents a family of hearing devices which can includethe group of cochlear implants, piezoelectric sound bridge transducersand the like. 100B represents a variety of neurostimulators and brainstimulators. Neurostimulators are used to stimulate the Vagus nerve, forexample, to treat epilepsy, obesity and depression. Brain stimulatorsare pacemaker-like devices and include electrodes implanted deep intothe brain for sensing the onset of the seizure and also providingelectrical stimulation to brain tissue to prevent the seizure fromactually occurring. The lead wires associated with a deep brainstimulator are often placed using real time MRI imaging. Most commonlysuch lead wires are placed during real time MRI. 100C shows a cardiacpacemaker which is well-known in the art. 100D includes the family ofleft ventricular assist devices (LVAD's), and artificial hearts,including the recently introduced artificial heart known as the Abiocor.100E includes an entire family of drug pumps which can be used fordispensing of insulin, chemotherapy drugs, pain medications and thelike. Insulin pumps are evolving from passive devices to ones that havesensors and closed loop systems. That is, real time monitoring of bloodsugar levels will occur. These devices tend to be more sensitive to EMIthan passive pumps that have no sense circuitry or externally implantedlead wires. 100F includes a variety of bone growth stimulators for rapidhealing of fractures. 100G includes urinary incontinence devices. 100Hincludes the family of pain relief spinal cord stimulators andanti-tremor stimulators. 100H also includes an entire family of othertypes of neurostimulators used to block pain. 100I includes a family ofimplantable cardioverter defibrillators (ICD) devices and also includesthe family of congestive heart failure devices (CHF). This is also knownin the art as cardio resynchronization therapy devices, otherwise knownas CRT devices. 100J illustrates an externally worn pack. This packcould be an external insulin pump, an external drug pump, an externalneurostimulator or even a ventricular assist device. 100K illustratesthe insertion of an external probe or catheter. These probes can beinserted into the femoral artery, for example, or in any other number oflocations in the human body. 100L illustrates one of various types ofEKG/ECG external skin electrodes which can be placed at variouslocations. 100M are external EEG electrodes placed on the head.

Referring now to FIG. 2, a prior art active implantable medical device(AIMD) 100 is illustrated. In general, the AIMD 100 could, for example,be a cardiac pacemaker 100C which is enclosed by a titanium housing 102as indicated. The titanium housing is hermetically sealed, however thereis a point where lead wires 104 must ingress and egress the hermeticseal. This is accomplished by providing a hermetic terminal assembly106. Hermetic terminal assemblies are well known and generally consistof a ferrule 108 which is laser welded to the titanium housing 102 ofthe AIMD 100. The hermetic terminal assembly 106 with its associated EMIfilter is better shown in FIG. 3. Referring once again to FIG. 2, fourlead wires are shown consisting of lead wire pair 104 a and 104 b andlead wire pair 104 c and 104 d. This is typical of what's known as adual chamber bipolar cardiac pacemaker.

The IS1 connectors 110 that are designed to plug into the header block112 are low voltage (pacemaker) connectors covered by an ANSI/AAMIstandard IS-1. Higher voltage devices, such as implantable cardioverterdefibrillators (ICDs), are covered by a standard known as the ANSI/AAMIDF-1. There is a new standard under development which will integrateboth high voltage and low voltage connectors into a new miniatureconnector series known as the IS-4 series. These connectors aretypically routed in a pacemaker application down into the rightventricle and right atrium of the heart 114. There are also newgeneration devices that have been introduced to the market that couplelead wires to the outside of the left ventricle. These are known asbiventricular devices and are very effective in cardiacresynchronization and treating congestive heart failure (CHF).

Referring once again to FIG. 2, one can see, for example, the bipolarlead wires 104 a and 104 b that could be routed, for example, into theright ventricle. The bipolar lead wires 104 c and 104 d could be routedto the right atrium. There is also an RF telemetry pin antenna 116 whichis not connected to the IS-1 or DS-1 connector block. This acts as ashort stub antenna for picking up telemetry (programming) signals thatare transmitted from the outside of the device 100.

It should also be obvious to those skilled in the art that all of thedescriptions herein are equally applicable to other types of AIMDs.These include implantable cardioverter defibrillators (using theaforementioned DF-1 connectors), neurostimulators (including deep brainstimulators, spinal cord stimulators, cochlear implants, incontinencestimulators and the like), and drug pumps. The present invention is alsoapplicable to a wide variety of minimally invasive AIMDs. For example,in certain hospital catheter lab procedures, one can insert an AIMD fortemporary use such as an ICD. Ventricular assist devices also can fallinto this type of category. This list is not meant to be limiting, butis only example of the applications of the novel technology currentlydescribed herein.

FIG. 3 is an enlarged, fragmented cross-sectional view taken generallyalong line 3-3 of FIG. 2. Here one can see in cross-section the RFtelemetry pin 116 and the bipolar lead wires 104 a and 104 c which wouldbe routed to the cardiac chambers by connecting these lead wires to theinternal connectors 118 of the IS-1 header block 112 (FIG. 2). Theseconnectors are designed to receive the plug 110 which allows thephysicians to thread lead wires through the venous system down into theappropriate chambers of the heart 114. It will be obvious to thoseskilled in the art that tunneling of deep brain electrodes orneurostimulator leads are equivalent.

Referring back to FIG. 3, one can see a prior art feedthrough capacitor120 which has been bonded to the hermetic terminal assembly 106. Thesefeedthrough capacitors are well known in the art and are described andillustrated in U.S. Pat. Nos. 5,333,095, 5,751,539, 5,905,627,5,959,829, 5,973,906, 5,978,204, 6,008,980, 6,159,560, 6,275,369,6,424,234, 6,456,481, 6,473,291, 6,529,103, 6,566,978, 6,567,259,6,643,903, 6,675,779, 6,765,780 and 6,882,248, all of which areincorporated herein by reference. In this case, a rectangular quadpolarfeedthrough capacitor 120 is illustrated which has an externalmetallized termination surface 122 and includes embedded electrode platesets 124 and 126. Electrode plate set 124 is known as the groundelectrode plate set and is terminated at the outside of the capacitor120 at the termination surface 122. These ground electrode plates 124are electrically and mechanically connected to the ferrule 108 of thehermetic terminal assembly 106 using a thermosetting conductivepolyimide or equivalent material 128 (equivalent materials will includesolders, brazes, conductive epoxies and the like). In turn, the hermeticseal terminal assembly 106 is designed to have its titanium ferrule 108laser welded 130 to the overall housing 102 of the AIMD 100. This formsa continuous hermetic seal thereby preventing body fluids frompenetrating into and causing damage to the electronics of the AIMD.

It is also essential that the lead wires 104 and insulator 136 behermetically sealed, such as by the gold brazes 132, 134 and 138. Thegold braze 132 wets from the titanium ferrule 108 to the alumina ceramicinsulator 136. In turn, the ceramic alumina insulator 136 is also goldbrazed at 134 to each of the lead wires 104. The RF telemetry pin 116 isalso gold brazed at 138 to the alumina ceramic insulator 136. It will beobvious to those skilled in the art that there are a variety of otherways of making such a hermetic terminal. This would include glasssealing the leads into the ferrule directly without the need for thegold brazes.

As shown in FIG. 3, the RF telemetry pin 116 has not been included inthe area of the feedthrough capacitor 120. The reason for this is thefeedthrough capacitor 120 is a very broadband single element low passEMI filter which would eliminate the desirable telemetry frequency,typically above 400 MHz.

FIG. 4 is a bottom view taken generally along line 4-4 in FIG. 3. Onecan see the gold braze 132 which completely seals the hermetic terminalinsulator 136 into the overall titanium ferrule 108. One can also seethe overlap of the capacitor attachment materials, shown as athermosetting conductive adhesive 128, which makes contact to the goldbraze 132 that forms the hermetic terminal 106.

FIG. 5 is an isometric view of the feedthrough capacitor 120. As one cansee, the termination surface 122 connects to the capacitor's internalground plate set 124. This is best seen in FIG. 6 where ground plate set124, which is typically screen printed onto ceramic layers, is broughtout and exposed to the termination surface 122. The capacitor's activeelectrode plate set 126 is illustrated in FIG. 7. In FIG. 6 one can seethat the lead wires 104 are in non-electrical communication with theground electrode plate set 124. However, in FIG. 7 one can see that eachone of the lead wires 104 is in electrical contact with the activeelectrode plate sets 126. The amount of capacitance is determined, inpart, by the overlap of the active electrode plate area 126 over theground electrode plate area. One can increase the amount of capacitanceby increasing the area of the active electrode plate set 126. One canalso increase the capacitance by adding additional layers. In thisparticular application, we are only showing six electrode layers: threeground plates 124 and three active electrode plate sets 126 (FIG. 3).However, 10, 60 or even more than 100 such sets can be placed inparallel thereby greatly increasing the capacitance value. Thecapacitance value is also related to the dielectric thickness or spacingbetween the ground electrode set 124 and the active electrode set 126.Reducing the dielectric thickness increases the capacitancesignificantly while at the same time reducing its voltage rating. Theserelationships are expressed ideally by the following equation:

${C = \frac{n\;\kappa\; A}{t}},$where n is the number of plate sets, κ is the dielectric constant of thematerial, A is the effective capacitive area, and t is the thicknessbetween opposing plates. This gives the designer many degrees of freedomin selecting the capacitance value.

FIG. 8 is a general diagram of a unipolar active implantable medicaldevice system 100. The housing 102 of the active implantable medicaldevice 100 is typically titanium, stainless steel or the like, and actsas one conductive electrode. Inside of the device housing are the AIMDelectronics. Usually AIMDs include a battery, but that is not always thecase. For example, a Bion may receive its energy from an externalpulsing magnetic field. A lead wire 104 is routed in insulativerelationship with the AIMD housing to a point 140 where it is embeddedin body tissue. In the case of a spinal cord stimulator 100H, the distalTIP 140 could be in the spinal cord. In the case of a deep brainstimulator 1008, the distal electrode 140 would be placed deep into thebrain tissue, etc. In the case of a cardiac pacemaker 100C, the unipolardistal electrode 140 would typically be placed in the cardiac rightventricle.

FIG. 9 is very similar to FIG. 8 except that it is a bipolar system. Inthis case, the return path is between the two distal electrodes 140 and140′. In the case of a cardiac pacemaker 100C, this would be known as abipolar lead wire system with one of the electrodes known as the distalTIP 142 and the other electrode which would float in the blood poolknown as the RING 144 (see FIG. 10). In contrast, the return path inFIG. 8 is between the distal electrode 140 through body tissue to theconductive housing 102 of the implantable medical device 100.

FIG. 10 further illustrates a bipolar lead wire system with a distal TIP142 and RING 144 typically as used in a cardiac pacemaker 100C In all ofthese applications, the patient could be exposed to the fields of an MRIscanner or other powerful emitter used during a medical diagnosticprocedure. RF currents that are directly induced in the lead wire system104 can cause heating by Ohmic (I²R) losses in the lead wire system orby heating caused by current flowing in body tissue. If these currentsbecome excessive, the associated heating can cause damage or evendestructive ablation to body tissue.

The distal TIP 142 is designed to be implanted adjacent to or affixedinto the actual myocardial tissue of the heart. The RING 144 is designedto float in the blood pool. In a pacemaker cardiac chamber, the blood isflowing (i.e. perfusion) and is thermally conductive, therefore RING 144structure is substantially cooled. However, the distal TIP 142 isthermally insulated by surrounding body tissue and can readily heat updue to the RF pulse currents of an MRI field. Accordingly, for a cardiacpacemaker application, the novel TANK concepts of the present inventionwill be more directed to the distal TIP 142 as opposed to the RING 144electrode (although the concepts of the present invention can be appliedto both). For poorly perfused areas, such as is typical inneurostimulator electrodes, then both TIP and RING electrodes must havea tank circuit of the present invention.

FIG. 11 is a schematic diagram showing an ideal parallel combination ofan inductor L and a capacitor C to be placed in the lead wire systems104 previously described. This combination forms an ideal parallel TANKcircuit filter 146 which will resonate at a particular frequency(f_(r)). (Ideal means that resistive losses have been omitted from themodel for simplicity).

FIG. 12 gives the frequency of resonance f_(r) for the parallel L-C TANKcircuit 146 of FIG. 11: where f_(r) is the frequency of resonance inHertz, L is the inductance in Henries and C is the capacitance inFarads. Clinical MRI systems vary in static field strength from 0.5Tesla all the way up to 3 Tesla with newer research machines going ashigh as 11.4 T. The frequency of the pulsed RF field associated with thestatic field is given by the Lamour Equation, f=γ_(H)T, where T is thefield strength in Teslas, and γ is gyromagnetic ratio for hydrogen,which is 42.58 MHz/T. Accordingly, a 3 Tesla MRI system has a pulsed RFfield of approximately 128 MHz.

By referring to FIG. 12, one can see that the resonant frequency fr ofan ideal TANK filter can be predicted by using the equation:

${f_{r} = \frac{1}{2\pi\sqrt{L\; C}}},$Where f_(r) is the resonant frequency, L is the inductance, in Henries,of the inductor component, and C is the capacitance, in Farads, of thecapacitor component. In this equation, there are three variables: f_(r),L, and C. The resonant frequency, f_(r), is a function of the MRI systemof interest. As previously discussed, a 1.5 T MRI system utilizes an RFsystem operating at approximately 64 MHz, a 3.0 T system utilizes a 128MHz RF, and so on. By determining the MRI system of interest, only L andC remain. By artificially setting one of these parameters, a filterdesigner needs only to solve for the remaining variable. This isillustrated in FIG. 12.

This equation, however, only deals with ideal inductor and capacitorelements. Real inductor and capacitor components exhibit seriesresistive elements, which are represented by the circuit diagram in FIG.16. These resistive components are due to material and designconsiderations, and are not necessarily independent of the respectiveinductive and capacitive values of the components.

By modeling the resistive elements with the reactive elements in acircuit modeling program such as P-Spice, one can see that the R_(L) andR_(C), as shown in FIG. 16, provide a significant contribution. As thetotal real resistance in the circuit increases, the 3 dB bandwidth ofthe TANK filter widens. This is a desired effect in this invention,since the widened 3 dB bandwidth corresponds to a broader range offiltered frequencies. For example, an ‘ideal’ TANK filter would resonateat only 64 MHz (for a 1.5 T MRI), and have no attenuation effect on a3.0 T MRI (128 MHz). However, a TANK filter with a real resistivecontribution would display a significant increase in the 3 dB bandwidth,and if a designer chose appropriate components, the TANK filter couldprovide filtering at both 64 MHz and 128 MHz.

This increase in filtering does not come without performance drawbacks.Since the energy dissipated by the TANK is finite, broadening thebandwidth of the TANK also has the effect of depressing the maximumattenuation of the circuit at resonance. If the attenuation drops toolow, filtering performance at MRI RF pulse frequency can be negativelyaffected.

Additionally, the series resistance of the inductor component is ofconcern. Since the inductor component is acting as the current path atlower frequencies, the series resistance should be as low as possible,so as to not filter out desirable low frequency biological signalsensing or therapy delivery signals. Because of this, it is preferred tochoose the inductive component first, then calculate the requiredcapacitive component. In this case, the left side of FIG. 12 should befollowed (resonance equation solved for C), to determine the neededcapacitor for the circuit.

In the preferred methodology, a relatively high inductance should bechosen (>100 nH). The selectivity of the TANK filter is determined bythe ratio of L/C. Accordingly, too low of an inductance value will notprovide the proper amount of attenuation or the proper 3 dB bandwidth atthe selected MRI pulsed frequency. Using the equation in FIG. 12, onecan see that the required capacitance to meet a 64 MHz system is 41 pF.However, it becomes obvious to one skilled in the art that a relativelylow series resistance is required of the inductor to guarantee lowattenuation at lower frequencies. Since the series resistance in aninductor is a function of the material properties and the designgeometry, careful component selection becomes critical.

Referring once again to FIG. 12, one can see that if the values of theinductor and the capacitor are selected properly, one could obtain aparallel TANK resonant frequency of 21.3 MHz (0.05 T), 64 MHz (1.5 T),128 MHz (3.0 T), and so on. Referring to FIG. 12, one can see thecalculations first assuming that the inductor value L is equal to 150nanohenries. The 150 nanohenries comes from the fact that given thesmall geometries involved inside of the human body, a very largeinductor is not practical. This is in addition to the fact that the useof ferrite materials or iron cores for such an inductor are undesirablefor two reasons: 1) the static magnetic field from the MRI scanner wouldalign the magnetic dipoles in such a ferrite and therefore make theinductor ineffective; and 2) the presence of ferrite materials willcause MRI image artifacts. This means that if one were imaging the rightventricle of the heart, for example, a fairly large area of the imagewould be blacked out due to the presence of these ferrite materials andthe way it interacts with the MRI field. It is also important that theinductor not vary while in the presence of the main static field.

It should be also noted that below resonance, particularly at very lowbiologic frequencies, the current in the lead wire system passes throughthe inductor element. Accordingly, it is important that the seriesresistance of the inductor element be quite low. Conversely, at very lowfrequencies, no current passes through the capacitor element. However,at high frequencies, the reactance of the capacitor element drops to amuch lower value, but there is no case (except for telemetry pins of anAIMD) where it is actually desirable to have high frequencies passthrough the TANK filter. Accordingly, for almost all applications, theresistive loss of the capacitor is not particularly important. This isalso known as the capacitor's equivalent series resistance (ESR). Acomponent of capacitor ESR is the dissipation factor of the capacitor (alow frequency phenomena). At frequencies well above resonance, it is notparticularly important how high the capacitor's dissipation factor oroverall ESR is when used as a component of a parallel TANK circuit 146as described herein.

Referring once again to FIG. 12, one can see the calculations forcapacitance by solving the resonant frequency f_(r) equation shown forC. Assuming an inductance value of 150 nanohenries, one can see that41.3 picofarads of capacitance would be required. Appropriate ceramicdielectrics that provide a high dielectric constant are well known inthe art and are very volumetrically efficient. They can also be made ofbiocompatible materials making them an ideal choice for use in thepresent invention.

FIG. 13 is a graph showing impedance versus frequency for the idealparallel TANK circuit 146 of FIG. 11. As one can see, using ideal (zeroresistance) circuit components, the impedance measured between points Aand B for the parallel TANK circuit 146 shown in FIG. 11 is zero untilone approaches the resonant frequency f_(r). At the frequency ofresonance, these ideal components combine together to approach aninfinite impedance. This comes from the equation Z_(ab) for theimpedance for the inductor in parallel with the capacitor shown as FIG.14. When the inductive reactance is equal to the capacitive reactance,the two imaginary vectors cancel each other and sum to zero. Referringto the equations in FIGS. 14 and 15, one can see in the impedanceequation for Z_(ab), that a zero will appear in the denominator whenX_(L)=X_(C). This has the effect of making the impedance approachinfinity as the denominator approaches zero. This means that at oneunique frequency, the impedance between points A and B in FIG. 11 willappear very high (analogous to opening a switch). Accordingly, it wouldbe possible, for example, in the case of a cardiac pacemaker, to designthe cardiac pacemaker for compatibility with one single popular MRIsystem. For example, in the patient literature, the device manual andperhaps contained in the digitally stored information on an implantedRFID chip, it could be noted that the pacemaker lead wire system hasbeen designed to be compatible with 3 Tesla MRI systems. Accordingly,with this particular device, a distal TIP TANK filter 146 would beincorporated where the L and the C values have been carefully selectedto be resonant at 128 MHz, presenting a high or almost infiniteimpedance at the MRI pulse frequency.

FIG. 16 is a schematic drawing of the parallel TANK circuit 146 of FIG.11, except in this case the inductor L and the capacitor C are notideal. That is, the capacitor C has its own internal resistance R_(C),which is otherwise known in the industry as dissipation factor orequivalent series resistance (ESR). The inductor L also has a resistanceR_(L). For those that are experienced in passive components, one wouldrealize that the inductor L would also have some parallel capacitance(C_(P)). This parasitic capacitance comes from the capacitanceassociated with adjacent turns. However, the inductance valuecontemplated is so low that one can assume that at MRI RF pulsefrequencies, the inductor's parallel capacitance is negligible. Onecould also state that the capacitor C also has some internal inductancewhich would appear in series. However, the novel capacitors describedherein are very small or coaxial and have negligible series inductance.Accordingly, the circuit shown in FIG. 16 is a very good approximationmodel for the novel parallel TANK circuits 146 as described herein.

This is best understood by looking at the FIG. 16 TANK circuit 146 atthe frequency extremes. At very low frequency, the inductive reactanceequation is X_(L)=2πfL. When the frequency f is close to zero (DC), thismeans that the inductor looks like a short circuit. It is generally thecase that biologic signals are low frequency, typically between 10 Hzand 1000 Hz. For example, in a cardiac pacemaker 100C, all of thebiologic frequencies of interest appear between 10 Hz and 1000 Hz. Atthese low frequencies, the inductive reactance X_(L) will be close tozero ohms. Over this range, on the other hand, the capacitive reactanceX_(C) which has the equation X_(C)=1/(2πfc) will look like an infiniteor open circuit. As such, at low frequencies, the impedance betweenpoints A and B in FIG. 16 will be substantially equal to R_(L).Accordingly, the resistance of the inductor (R_(L)) should be kept assmall as possible to minimize attenuation of biologic signals orattenuation of electrical stimulation pulses to body tissues. This willallow biologic signals and pacing pulses to pass through the TANK filter146 freely. It also indicates that the amount of capacitive loss R_(C)is not particularly important. As a matter of fact, it would bedesirable if that loss were fairly high so as to not freely pass veryhigh frequency signals (such as undesirable EMI from cellular phones).It is also desirable to have the Q of the circuit shown in FIG. 16carefully balanced so that the TANK frequency bandwidth can be a littlewider. In other words, in a preferred embodiment, it would be possibleto have a TANK wide enough to block both 64 MHz and 128 MHz therebymaking the medical device compatible for use in both 1.5 Tesla and 3Tesla MRI systems.

FIG. 17 is a drawing of the unipolar AIMD lead wire system, previouslyshown in FIG. 8, with the TANK filter 146 of the present invention addednear the distal electrode 140. As previously described, the presence ofthe TANK circuit 146 will present a very high impedance at one or morespecific MRI RF pulse frequencies. This will prevent currents fromcirculating through the distal electrode 140 into body tissue at thisselected frequency(s). This will provide a very high degree of importantprotection to the patient so that distal TIP heating does not causetissue damage.

Referring once again to FIG. 17, one can see that an optional RFID tag260 has been placed at the lead wire near the active implantable medicaldevice. U.S. patent application Ser. No. 11/307,145, filed Jan. 25,2006, the contents of which are incorporated herein, describes how toplace RFID tags and hermetically seal them in the header block of acardiac pacemaker or the like. It is common in the art that “mix andmatch” goes on between the implantable medical device and the lead wiresystems. This is particularly true for cardiac pacemakers. For example,it is very common that a St. Jude pacemaker could be used with Medtroniclead wires and vice versa. It is also common that lead wires will stayimplanted in the human body much longer than the actual activeimplantable medical device. For example, a pacemaker patient may havelead wires implanted for forty years or longer where the pacemakeritself is replaced in the pectoral pocket and plugged in every five toseven years. The TANK filter of the present invention is designed towork with any model pacemaker to prevent overheating during MRIprocedures of the lead wires and its associated distal TIP. Accordingly,it is very important over time that a hospital or MRI lab be able toidentify which patients have MRI compatible lead wire systems and whichdo not. It is a feature of the present invention that an RFID tag 260can be affixed to or placed adjacent to an implantable device or in theelectrode wire system so it can be appropriately identified. The RFIDtag 260 could also include important information such as the resonantfrequency that the distal TIP TANK was designed for. For example, theRFID tag 260 could emit a pulse indicating that it is RFID compatible at1.5 T (64 MHz). It is important that the active implantable medicaldevice also incorporate robust EMI filters such that the RFID emitter(reader or scanner) not interfere with the electronics of the AIMDitself. An ideal RFID frequency for the present invention would be 13.56MHz which would readily penetrate body tissue and be detected by theRFID tag 260 that is attached to the lead wire. There are a variety offixation methods that can be used to attach the RFID tag 260 to the leadwire, including bonding within the encapsulation material of the leadwire itself or by using a tie or suture attachment. It is not evennecessary that the RFID tag 260 be directly attached to the lead wiresthemselves. For example, it is also known in the art that RFID tags canbe injected anywhere in the human body, for example, near the wrist. Inthis case, the RFID tag 260 would include important information aboutthe presence and MRI compatibility of the lead wire system and/or theAIMD itself. A company called Verichip already has implantable RFID tagsfor both animal and human identification. A problem with Verichip andother prior art RFID tags is that they are not truly hermetic. Novelhermetically sealed canisters to hold RFID chips is disclosed in U.S.application Ser. No. 11/307,145, filed Jan. 25, 2006, the contents ofwhich are incorporated herein by reference. Because of the potentiallength of implant AIMD lead wire systems (for example, cochlear orpacemaker lead wires that could be implanted for 40 years or evenlonger), it is very important that the implanted RFID tag be reliableover a long period of time. This means that it has to be truly hermeticto a leak rate that at least exceeds 1×10⁻⁷ cc per second. Accordingly,the hermetic assemblies as described in the U.S. application Ser. No.11/307,145 are the preferred embodiment.

FIG. 18 is an ideal representation of the novel TANK filter 146 usingswitches to illustrate its function. Inductor L has been replaced with aswitch S_(L). When the impedance of the inductor is quite low, theswitch S_(L) will be closed. When the impedance or inductive reactanceof the inductor is high, the switch S_(L) will be shown open. There is acorresponding analogy for the capacitor element C. When the capacitivereactance looks like a very low impedance, the capacitor switch S_(C)will be shown closed. When the capacitive reactance is shown as a veryhigh impedance, the switch S_(C) will be shown open. This analogy isbest understood by referring to FIGS. 19, 20 and 21.

FIG. 19 is the low frequency model of the TANK filter 146. At lowfrequencies, capacitors tend to look like open circuits and inductorstend to look like short circuits. Accordingly, switch S_(L) is closedand switch S_(C) is open. This is an indication that at frequenciesbelow the resonant frequency of the TANK filter 146 currents will flowthrough the inductor element. This is an important consideration for thepresent invention that low frequency biological signals not beattenuated. For example, in a cardiac pacemaker, frequencies of interestgenerally fall between 10 Hz and 1000 Hz. Pacemaker pacing pulses fallwithin this general frequency range. In addition, the implantablemedical device is also sensing biological frequencies in the samefrequency range. Accordingly, such signals must be able to flow readilythrough the TANK filter's inductor element. A great deal of attentionshould be paid to the inductor design so that it has a very high qualityfactor (Q) and a low parasitic series resistance.

FIG. 20 is a model of the novel TANK filter 146 at its resonantfrequency. By definition, when a parallel TANK circuit is at resonance,it presents a very high impedance to the overall circuit. Accordingly,both switches S_(L) and S_(C) are shown open. For example, this is howthe TANK filter 146 prevents the flow of MRI currents through pacemakerlead wires and/or into body tissue at a selected MRI RF pulsedfrequency.

FIG. 21 is a model of the TANK filter 146 at high frequency. At highfrequencies, inductors tend to look like open circuits. Accordingly,switch S_(L) is shown open. At high frequencies, ideal capacitors tendto look like short circuits, hence switch S_(C) is closed. It should benoted that real capacitors are not ideal and tend to degrade inperformance at high frequency. This is due to the capacitor's equivalentseries inductance and equivalent series resistance. Fortunately, for thepresent invention, it is not important how lossy the capacitor element Cbecomes at high frequency. This will only serve to attenuate unwantedelectromagnetic interference, for example, from cell phones, fromflowing in the lead wire system. Accordingly, the quality factor of thecapacitor element C is not nearly as important as the quality factor ofthe inductor element L. The equation for inductive reactance (X_(L)) isgiven in FIG. 15. The capacitor reactance equation (X_(C)) is also givenin FIG. 15. As one can see, when one inserts zero for the frequency, onederives the fact that at very low frequencies inductors tend to looklike short circuits and capacitors tend to look like open circuits. Byinserting a very high frequency into the same equations, one can seethat at very high frequency ideal inductors look like an infinite oropen impedance and ideal capacitors look like a very low or shortcircuit impedance.

FIG. 22 is the bipolar system of FIG. 9 redrawn to show two novel TANKfilters 146 in each lead wire 104, 104′. In this case, there is a TANKcircuit F_(r1) consisting of L₁ and C₁ in both of the bipolar lead wires104, 104′, which is designed to resonate at one selected frequency. Fora 1.5 Tesla MRI system, this would be 64 MHz. These are then placed inseries with a second set of TANK filters 146′ which are designed toresonate at F_(r2). These consist of L₂, C₂ parallel inductor capacitorcombinations. These could be designed for operation in a 3 Tesla MRIsystem and would therefore be designed to resonate at 128 MHz. In thisway, currents would be blocked from both types of MRI systems. The tradeoff in this example is that the distal electrodes 140, 140′ would bephysically elongated due to the additional components necessary. An RFIDchip, such as that described in relation to FIG. 17, could be associatedwith each 104, 104′ lead wire so as to identify each electrode or leadwire 104, 104′ as incorporating a TANK filter 146, in accordance withthe present invention. Alternatively, a single RFID chip could beassociated with either lead wire 104, 104′ or anywhere in the patient,so as to identify both of the lead wires 104 and 104′ as incorporatingTANK filters 146.

FIG. 23 is a decision tree block diagram that better illustrates thedesign process herein. Block 148 is an initial decision step thedesigner must make. For illustrative purposes, we will start with avalue of capacitance that is convenient. This value of capacitance isgenerally going to relate to the amount of space available in the AIMDlead wire system and other factors. These values for practical purposesgenerally range in capacitance value from a few tens of picofarads up toabout 10,000 picofarads. This puts practical boundaries on the amount ofcapacitance that can be effectively packaged within the scope of thepresent invention. However, that is not intended to limit the generalprinciples of the present invention, but just describe a preferredembodiment. Accordingly, in the preferred embodiment, one will selectcapacitance values generally ranging from 10 picofarads up to about 4000picofarads and then solve for a corresponding inductance value requiredto be self-resonant at the selected telemetry frequency. Referring backto FIG. 23, one makes the decision whether the design was C first or Lfirst. If one makes a decision to assume a capacitance value C firstthen one is directed to the left to block 150. In block 150, one does anassessment of the overall packaging requirements of a distal TIP 142TANK filter 146 and then assumes a realizable capacitance value. So, indecision block 150, we assume a capacitor value. We then solve theresonant TANK equation f_(r) from FIG. 12 at block 152 for the requiredvalue of inductance (L). We then look at a number of inductor designs tosee if the inductance value is realizable within the space and otherconstraints of the design. If the inductance value is realizable, thenwe go on to block 154 and finalize the design. If the inductance valueis not realizable within the physical and practical constraints, then weneed to go back to block 150 and assume a new value of capacitance. Onemay go around this loop a number of times until one finally comes upwith a compatible capacitor and an inductor design. In some cases, onewill not be able to achieve a final design using this alone. In otherwords, one may have to use a custom capacitor value or design in orderto achieve a result that meets all of the design criteria. That is, acapacitor design with high enough internal losses R_(C) and an inductordesign with low internal loss R_(L) such that the TANK filter 146 hasthe required quality factor (Q), has sufficient band width (but not toomuch), that it be small enough in size, that it have sufficient currentand high voltage handling capabilities and the like. In other words, onehas to consider all of the design criteria in going through thisdecision tree.

In the case where one has gone through the left hand decision treeconsisting of blocks 150, 152 and 154 a number of times and keeps comingup with a “no,” then one has to assume a realizable value of inductanceand go to the right hand decision tree starting at block 156. One thenassumes a realizable value of inductance (L) with a low enoughequivalent series resistance for the inductor R_(L) such that it willwork and fit into the design space and guidelines. After one assumesthat value of inductance, one then goes to decision block 158 and solvesthe equation C in FIG. 12 for the required amount of capacitance. Afterone finds the desired amount of capacitance C, one then determineswhether that custom value of capacitance will fit into the designparameters. If the capacitance value that is determined in step 160 isrealizable, then one goes on and finalizes the design. However, if it isnot realizable, then one can go back up to step 156, assume a differentvalue of L and go through the decision tree again. This is done over andover until one finds combinations of L and C that are practical for theoverall design. For purposes of the present invention, it is possible touse series discrete inductors or parallel discrete capacitors to achievethe same overall result. For example, in the case of the inductorelement L, it would be possible to use two, three or even more (n)individual inductor elements in series. The same is true for thecapacitor element that appears in the parallel TANK filter 146. Byadding or subtracting capacitors in parallel, we are also able to adjustthe total capacitance that ends up resonating in parallel with theinductance.

It is also possible to use a single inductive component that hassignificant parasitic capacitance between its adjacent turns. A carefuldesigner using multiple turns could create enough parasitic capacitancesuch that the coil becomes self-resonant at a predetermined frequency.In this case, the predetermined frequency would be the MRI pulsedfrequency.

Efficiency of the overall TANK circuit 146 is also measured in terms ofa quality factor, Q, although this factor is defined differently thanthe one previously mentioned for discrete capacitors and inductors. Thecircuit Q is typically expressed using the following equation:

$Q = \frac{f_{r}}{\Delta\; f_{3d\; B}}$Where f_(r) is the resonance frequency, and Δf_(3dB) shown as points aand b in FIG. 24, is the bandwidth of the TANK filter 146. Bandwidth istypically taken as the difference between the two measured frequencies,f₁ and f₂, at the 3 dB loss points as measured on an insertion losschart, and the resonance frequency is the average between f₁ and f₂. Ascan be seen in this relationship, higher Q values result in a narrower 3dB bandwidth.

Material and application parameters must be taken into considerationwhen designing TANK filters. Most capacitor dielectric materials age1%-5% in capacitance values per decade of time elapsed, which can resultin a shift of the resonance frequency of upwards of 2.5%. In a high-Qfilter, this could result in a significant and detrimental drop in TANKperformance. A low-Q filter would minimize the effects of resonanceshift and would allow a wider frequency band through the filter.However, low Q filters also display lower than desirable attenuationbehavior at the desired TANK frequency (see FIG. 24, curve 162). Forthis reason, the optimum Q for the TANK filter of the present inventionwill embody a high Q inductor L and a relatively low Q capacitor C whichwill result in a medium Q TANK filter as shown in curve 164 of FIG. 24.

Accordingly, the “Q” or quality factor of the TANK circuit is veryimportant. As mentioned, it is desirable to have a very low loss circuitat low frequencies such that the biological signals not be undesirablyattenuated. The quality factor not only determines the loss of thefilter, but also affects its 3 dB bandwidth. If one does a plot of thefilter response curve (Bode plot), the 3 dB bandwidth determines howsharply the filter will rise and fall. With reference to curve 166 ofFIG. 24, for a TANK that is resonate at 128 MHz, an ideal response wouldbe one that had infinite attenuation at 128 MHz, but had zeroattenuation at low frequencies below 1 KHz. Obviously, this is notpossible given the space limitations and the realities of the parasiticlosses within components. In other words, it is not possible (other thanat cryogenic temperatures) to build an inductor that has zero internalresistance. On the other hand, it is not possible to build a perfect(ideal) capacitor either. Capacitors have internal resistance known asequivalent series resistance and also have small amounts of inductance.Accordingly, the practical realization of a circuit, to accomplish thepurposes of the present invention, is a challenging one. This isparticularly true when one also considers that the tank circuit mustalso be miniature, highly reliable, and completely biocompatible.

The performance of the circuit is directly related to the efficiency ofboth the inductor and the capacitor; the less efficient each componentis, the more heat loss that results, and this can be expressed by theaddition of resistor elements to the ideal circuit diagram. The effectof lower Q in the TANK circuit is to broaden the resonance peak aboutthe resonance frequency. By deliberately using a low Q capacitor, onecan broaden the resonance such that relatively high impedance (highattenuation) is presented at multiple MRI RF frequencies, for example 64MHz and 128 MHz.

Referring again to FIG. 24, one can see curve 164 wherein a high Qinductor has been used in combination with a low Q capacitor. This has avery desirable effect in that at very low frequencies, the impedance ofthe TANK circuit 146 is essentially zero (below 1 ohm) ohms (or zero dBloss). This means that biologic frequencies are not undesirablyattenuated. However, one can see that the 3 db bandwidth is much larger.This is desirable as it will block multiple RF frequencies. As one goeseven higher in frequency, curve 164 will desirably attenuate other highfrequency EMI signals, such as those from cellular telephones, microwaveovens and the like. Accordingly, it is often desirable that very lowloss inductors be used in combination with relatively high losscapacitors to achieve a medium or lower Q TANK filter. Again referringto FIG. 24, one can see that if the Q of the overall circuit or of theindividual components becomes too low, then we have a seriousdegradation in the overall attenuation of the TANK filter. Accordingly,a careful balance between component design and TANK circuit Q must beachieved.

FIG. 25 is a tracing of an actual patient X-ray from the Association forthe Advancement of Medical Instrumentation (AAMI) PC69 Pacemaker EMCTask Force. This particular patient required both a cardiac pacemaker100C and an implantable cardioverter defibrillator 100I. Thecorresponding lead wire system 104, as one can see, makes for a verycomplicated antenna and loop coupling situation. The reader is referredto the article entitled, “Estimation of Effective Lead Loop Area forImplantable Pulse Generator and Implantable Cardioverter Defibrillators”provided by the AAMI Pacemaker EMC Task Force.

Referring again to FIG. 25, one can see that from the pacemaker 100C,there are electrodes in both the right atrium and in the rightventricle. Both these involve a TIP and RING electrode. In the industry,this is known as a dual chamber bipolar lead wire system. Accordingly,at a minimum the TANK filters 146 of the present invention should beplaced at the distal TIP in the right atrium and the distal TIP in theright ventricle from the cardiac pacemaker. One can also see that theimplantable cardioverter defibrillator (ICD) 100I is implanted directlyinto the right ventricle. Its shocking TIP and sense electrodes wouldalso require a TANK filter so that MRI exposure cannot induce excessivecurrents in that lead wire system. Modern implantable cardioverterdefibrillators (ICDs) incorporate both pacing and cardioverting (shock)features. Accordingly, it is becoming quite rare for a patient to havetwo discrete AIMD systems, as shown in FIG. 25. However, the number ofelectrodes remain the same. There are also newer combined pacemaker/ICDsystems which include biventricular pacemaking (pacing of the leftventricle). These systems can have as many as nine to even twelve leadwires.

FIG. 26 is a line drawing of an actual patient cardiac X-ray of one ofthe newer bi-ventricular lead wire systems. The new bi-ventricularsystems are being used to treat congestive heart failure, and make itpossible to implant leads outside of the left ventricle. This makes fora very efficient pacing system; however, the lead wire system 104 isquite complex. When a lead wire system 104, such as those described inFIGS. 8, 9, 10 and 11, are exposed to RF fields, electric currents canbe induced into such lead wire systems. For the bi-ventricular system,TANK filters 146 would be required at each of the three distal TIPs.

FIG. 27 illustrates a single chamber bipolar cardiac pacemaker lead wireshowing the distal TIP 142 and the distal RING 144 electrodes. This is aspiral wound (coaxial) system where the RING coil 104 is wrapped aroundthe TIP coil 104′. There are other types of pacemaker lead wire systemsin which these two leads lay parallel to one another (known as a bifilarlead system).

FIG. 28 is a schematic illustration of the area 28-28 in FIG. 27. In thearea of the distal TIP 142 and RING 144 electrodes, TANK filters 146 and146′ have been placed in series with each of the respective RING and TIPcircuits. The RING circuit wire 104 has been drawn straight instead ofcoiled for simplicity. Accordingly, at an MRI pulsed RF frequency, ahigh impedance will be presented thereby reducing or stopping the flowof undesirable MRI induced RF current.

The TIP 142 is designed to be inserted into intimate contact withmyocardial tissue. Over time it becomes encapsulated and fully embeddedor buried within such tissue. However, the RING 144 is designed to floatwithin the blood pool, for example, in the ventricle or atrium. With theconstant blood perfusion, the RING 144 is somewhat cooled during medicaldiagnostic procedures, such as MRI. However, the TIP 142 which isembedded in the myocardial tissue, is thermally insulated in comparison.It can't always be assumed that a RING electrode that is floating in theblood pool will be adequately cooled by the flow of blood. There arecertain types of patients that have illnesses that lead to very lowblood flow rates and perfusion issues. Accordingly, in a preferredembodiment both the distal TIP and the RING would both be filtered withthe TANK of the present invention. Accordingly, the operation of thenovel TANK filter 146 is more important in the TIP 142 than it is in theRING 144 in order to prevent distal TIP heating and associated tissuedamage. In most cardiac applications, only a TIP TANK filter is requiredfor MRI compatibility.

FIGS. 29 and 30 illustrate a prior art tubular feedthrough capacitor168. In the art, this is known as a single wall or extruded tubularcapacitor, and is very commonly used in commercial electronicapplications. Such capacitors 168 are fabricated in a drawing-extrusionprocess. The tubes are cut off at a desired length and are fired(sintered). The material in this case is a high K ceramic dielectric170. The tube 170 is then metallized on the outside 172 and alsometallized on the inside diameter 174 as illustrated. The capacitance isformed between the inner and outer diameter metallizations 172, 174 (twoconcentric cylinders separated by the high K dielectric). A flange 176is typically associated with capacitor 168 by high temperature solderattachment 178 for convenient mounting into a bulkhead. There is also alead wire 180 which passes continuously through the feedthroughcapacitor 168 and is attached to the inside diameter metallization 174using a high temperature solder 182. This continuous lead wiredistinguishes all prior art feedthrough capacitors from the present TANKinvention which always features a novel discontinuous lead. These priorart feedthrough capacitors are very efficient low inductance capacitorsand, as mentioned, are used in a wide variety of prior art electroniclow pass EMI filter applications.

FIG. 31 is a cross-section of a prior art multilayer tubular capacitor184. This is very similar to the capacitor 168 shown in FIG. 30 exceptthat it is not formed by tube extrusion processes. This capacitor 184 isrolled, has embedded electrode plates 186, 188, and has a cylindricalshape. It is then fired and metallization is placed on its top end 190and bottom end 192 as shown. An electrical connection 194 is made tolead wire 196. Metallization 192 is attached to the electrode set 188 atthe bottom of the cross-section. An optional flange 198 is added forconvenient mounting into a bulkhead. This flange is attached using hightemperature solder, braze, or the like 200.

FIG. 32 is a modification of the prior art single wall tubular capacitor168 illustrated in FIGS. 29 and 30 showing the features of the presentinvention. In FIG. 32, one can see that there is a lead wire 180 whichis a lead wire coming from an active implantable medical device 100 (notshown). The distal TIP 142 makes contact with body tissue. In this case,this could be the distal TIP 142 in the ventricle of a cardiacpacemaker.

FIG. 33 is an inverted view of the high surface area distal TIP 142shown in FIG. 32 (passive fixation wings not shown). There are a numberof distal TIPs that are common in the art. Generally, these are of veryhigh surface area to optimize electrical performance with body tissue.These are known as low polarization TIPs. Some of these TIP designs areeven designed to elute certain drugs to minimize tissue inflammation,necrosis, etc.

FIG. 34 illustrates an alternative to the inverted distal TIP previouslyillustrated in FIG. 33. FIG. 34 is known in the art as an activefixation helix TIP 142′ whose sharp point 204 and helix coil aregenerally designed to be threaded into body tissue. The TIP 142′includes a base plate 202 generally consisting of a biocompatiblematerial, such as platinum, titanium or the like, and a helix lead wire204 generally attached to the base plate by laser welding 206.

The novel structure illustrated in FIG. 32 is better understood bylooking at the cross-section in FIG. 35 taken generally along the lines35-35 from FIG. 32. Referring to FIG. 35 and comparing it with FIG. 30,one can see that there is a significant difference between the two.First of all, the novel lead wire 180 is discontinuous in that it doesnot pass all the way through the center of the feedthrough capacitor168. Instead, it has been replaced by the inductive structure 208. It isdesirable, but not required, that structure 208 be an air wound orequivalent non-ferrous inductor. In this case, the air wound coil isinside of the tubular capacitor element and is thereby protected bydirect exposure to body fluids. As previously described, embeddinginductor coils in body fluid is problematic because of the varyingdielectric constant of the body fluid and also its electricalconductivity properties. However, the present application also has broadapplication to a variety of non-medical implant applications, includingmilitary, space and various other commercial applications. Accordingly,the inductor 208 could also include the group of a toroidal inductor, asolenoid inductor wound around a ferrite or iron or other ferro-magneticcore, a ferrite chip inductor involving various ferro-magneticmaterials, and the like. As previously mentioned, the use of theseferro-magnetic materials in the presence of an MRI system is not ideal.The reason for this is that ferromagnetic materials exhibit hystereticbehavior, which results in changing electrical performance in highmagnetic fields. In addition, substantial MRI image artifact would alsobe induced. However, for a non-medical application, there is no reasonwhy the inductor L could not be made from a variety of materials. Onecan also see that the device has been integrated with coaxial TIP 142such that it is ready for implantation into a ventricle or atrium of acardiac patient.

The ideal schematic diagram for the novel TANK filter 146 of FIGS. 32and 35 is shown in FIG. 36. As previously mentioned, the values of C(168) and L (208) are carefully selected to be resonant such that a highimpedance L-C TANK filter is achieved at a selected MRI pulse frequencyor band of frequencies.

Referring once again to FIG. 35, one can see that an electricalconnection is required between lead wire 180 and a conductive end cap210 which is shown electrically attached to the capacitor insidediameter metallization 174 at point 182. There is also an electricalconnection required between the distal TIP 142 and the capacitor outsidediameter metallization 172 at point 178. There is also an electricalconnection 183 required between the inductor spiral 208 and theconductive distal TIP 142. This electrical connection places theinductor element 208 in parallel with the capacitor element 170 therebyforming the novel tank of the present invention. Again, lead wire 180 isdiscontinuous to the distal TIP 142 with said discontinuity replaced bythe inductor spiral 208. It is very important that all of the electricalconnections be of suitable biocompatible materials. For example,electrical connection 181 could be of a suitable laser weld. Electricalconnection 182 and 183 could be of biocompatible thermosettingconductive adhesives such as gold or platinum flake loaded silicones,polyimides or the like. The gap 212 shown between the distal TIP 142 andthe inside diameter metallization 174 can be air, but it is preferablyan insulator such as a biocompatible plastic thermo-setting polymer, orthe like.

FIG. 37 is a cross-sectional drawing incorporating the prior artmultilayer capacitor 184 previously described in FIG. 31. Referring toFIG. 37, one can see that the lead wire 196 is discontinuous. In fact,the lead wire 196 is terminated at point 214 where it attaches to theinternal inductor 208, which can be an air wound spiral type inductor asillustrated in other applications, or a ferrite chip inductor or thelike. The inductor could also be wound around the outside around thecapacitor 184. As previously discussed, winding the inductor around theoutside of the capacitor would have directly exposed its turns to bodyfluid, which would be undesirable. Body fluid is relatively conductiveand would cause currents to flow from turn to turn. In addition, thedielectric constant of the body fluid would change the parasiticcapacitance between turns and thereby affect the resonant frequency ofthe parallel tank. There is an electrical and mechanical attachment 194between lead wire 196 and the capacitor top metallization layer 190.This metallization contacts electrode plate set 186. At the opposite endof the multilayer tubular capacitor structure 184, there is a distal TIPelectrode 142. This is electrically attached to the inductor 208 atpoint 216. There is also an electrical attachment to the oppositeelectrode plate set 188 through capacitor termination layer 192. Thishas the effect of taking the capacitance formed by the multilayercapacitor 184 and putting it in parallel with the inductance. This isbest understood by referring to the schematic diagram in FIG. 38. For aspecific dielectric constant material, the capacitance value is adjustedby the relative overlapping area of the electrode plate sets 186 and 188and the dielectric spacing thickness between them. In other words, onecan design this to have any capacitance value desired, so that it willself-resonate with the inductor at specific frequencies. An optionalinsulative washer 218 is disposed between the metallization 192 and thedistal TIP 142.

FIG. 39 illustrates a prior art unipolar discoidal feedthrough capacitor220. This is a multilayer coaxial capacitor which is well known in theprior art. One of its advantages is that it operates at very highfrequency. This is because of its coaxial transmission line nature andthe fact that it has very low internal inductance. The capacitor 220includes overlapping circular electrode plate sets 222 and 224.Electrode plate set 222 is known as the active electrode plate set andis electrically connected to the capacitor inside diameter metallization226 as shown. The ground electrode plate set 224 is attached to theoutside diameter metallization 228. Such prior art feedthroughcapacitors are often used in conjunction with EMI filters for activeimplantable medical devices. These are generally shown and described inU.S. Pat. Nos. 4,424,551; 5,905,627; 6,008,980; 6,643,903; 6,765,779 andmany others.

FIG. 40 shows the prior art feedthrough capacitor 220 of FIG. 39 mountedto a ferrule 230 of hermetic terminal 232 of an active implantablemedical device housing 234. In all prior art devices, lead wire 238 iscontinuous. The hermetic terminal 232 is attached to, typically, atitanium housing 234, for example, of a cardiac pacemaker. An insulator236, like alumina ceramic or glass, is disposed within the ferrule 230and forms a hermetic seal against body fluids. A terminal pin or leadwire 238 extends through the hermetic terminal 232, passing throughaligned passageways through the insulator 236 and the capacitor 220. Agold braze 240 forms a hermetic seal joint between the terminal pin 238and the insulator 236. Another gold braze 242 forms a hermetic sealjoint between the alumina insulator 236 and the titanium ferrule 230. Alaser weld 244 provides a hermetic seal joint between the ferrule 230and the housing 234. The feedthrough capacitor 220 is shown surfacemounted in accordance with U.S. Pat. No. 5,333,095, and has anelectrical connection 246 between its inside diameter metallization 226and hence the active electrode plate set 222 and lead wire 238. There isalso an outside diameter electrical connection 248 which connects thecapacitor's outside diameter metallization 228 and hence the groundelectrodes 224 to the ferrule 230. Feedthrough capacitors are veryefficient high frequency devices that have minimal series inductance.This allows them to operate as EMI low-pass filters over very broadfrequency ranges.

FIG. 41 is the schematic diagram of the prior art feedthrough capacitor220 illustrated in FIGS. 39 and 40.

FIG. 42 is a novel adaptation of the prior art feedthrough capacitor ofFIGS. 39 and 40 in accordance with the present invention. An end cap 250is seated over the top of the feedthrough capacitor 220 such that itmakes electrical contact at point 252 with the capacitor outsidediameter metallization 228. There is a space or air gap 254 whichseparates the end cap 250 from the capacitor inside diametermetallization 226 so that a short circuit does not occur. In a preferredembodiment the gap 254 would be filled with an insulative material suchas a non-conductive epoxy or thermal setting polymer or a spacer disksuch as a silicone disk or other biocompatible material. Referring onceagain to FIG. 42, one can see that there is a novel inductor 208contained within the capacitor 220 inside diameter. As will be morefully discussed herein, the inductor 208 can be an air wound spiral,chip inductors and the like. The lead wire system 238 and 238′ in thiscase, is discontinuous. That is, unlike other prior art feedthroughcapacitors, the lead wire 238 does not pass all the way through thecenter of the capacitor 220. The inductor 208 is connected to the endplate 250 at location 256. The inductor 208 is also connected to theother lead wire segment 238′ at the opposite end at point 258.Biocompatible electrical and mechanical attachments at points 256 and258 can be accomplished by laser welding, brazing, mechanicalattachments and the like. In general, the use of solders is undesirablein that they are generally not considered biocompatible. An exception tothis would be to surround the entire structure shown in FIG. 42 with aglass encapsulant or sapphire to hermetically seal the entire assemblyand thereby prevent body fluids from reaching this TANK filter structure(see FIG. 140 for example). Referring once again to the bottom of thenovel feedthrough capacitor 220 of FIG. 42, one can see that lead wire238′ has been terminated with a convenient nail head shape so thatelectrical connection 246 can be made from the lead wire 238′ to thecapacitor's inside diameter metallization 226. This forms the novelfilter TANK circuit 146 consisting of the parallel inductor 208 andcapacitor 220 as shown in the schematic in FIG. 43. A particularadvantage of the structure shown in FIG. 42 is that high volumemanufacturing techniques that are presently employed for ceramicfeedthrough capacitors can be used. With the exception of thediscontinuous lead, there is nothing structurally different about thefeedthrough capacitor itself as compared with the prior art capacitor220 of FIG. 39. In other words, this is a novel adaptation offeedthrough capacitors for convenient use in a TANK filterconfiguration, for example, in the distal TIP 142 of implantable medicaldevices. The miniature coaxial structure of such capacitors is ideal forinsertion, for example, through veins or tunneling through body tissue.

Referring once again to FIG. 42, one can see that the capacitor 220 andthe inductor 208 and the end cap 250 are all exposed to body fluids.This is also true of all of the various electrical connections. It isvery important that all of these materials be long term biocompatible,as disclosed in U.S. Pat. No. 7,113,387 which is incorporated byreference herein. Referring once again to FIG. 42, one can see that thecapacitor 220 would be composed of biocompatible materials as describedin U.S. Pat. No. 7,113,387. In a preferred embodiment, the capacitorelectrodes would be of either high-fired pure platinum or a ternarysystem consisting of gold, platinum and palladium. The capacitor'sterminations 228 would be of pure gold or platinum plating or a loadedglass frit. The same would be true of the inside diameter capacitortermination 226. The end plate 250 would be of platinum, platinumiridium, titanium or other suitable biocompatible material. Thediscontinuous lead wires 238 and 238′ would be comprised of MP-35N orequivalent. The electrical connections 256 would generally consist oflaser welding and not introduce foreign materials at all. Electricalconnection material 252 and 246 would be of a suitable thermallyconductive biocompatible material. Examples of this would be gold orplatinum flake loaded ISO qualified silicones, polyimides, thermalsetting polymers and the like.

FIG. 44 is very similar to FIG. 42 except that instead of being placedin the midpoint or other location of a lead wire system, the novel L-CTANK now terminates in distal TIP 142. The distal TIP 142 is designedfor direct contact with, in the case of a cardiac pacemaker, myocardialtissue. All of the other features of the TANK filter 146 of FIG. 44 arevery similar to the structure of the TANK filter 146 of FIG. 42.

FIG. 45 is the schematic diagram of the distal TIP TANK circuit 146 ofthe substrate shown in FIG. 44.

FIG. 46 shows yet another novel arrangement wherein any of the novelTANK circuits 146 as previously described herein can also be placedinside the housing 234 of the active implantable medical device. Anadvantage to this is that the TANK inductor and capacitor components arecompletely protected from body fluid. For example, the novel feedthroughcapacitor arrangement as previously described in FIG. 42, could beplaced inside the active implantable medical device. These particular LCTANK filters 146 could be placed at the distal TIP and/or anywhere alongthe lead wire system as well as inside the active implantable medicaldevice itself. This is also true for the TANK filters 146 shown in FIG.32, 35 or 37. In other words, any of the TANK L-C filters of the presentinvention can be conveniently located inside the active implantablemedical device 100. In actual practice, it may be required to havedistal electrode TIP TANK filters 146 in addition to TANK filters 146installed inside the AIMD. In another embodiment, it would be possibleto have a distal TIP tank filter placed inside the AIMD, one or moredistal TIP tanks placed along the associated lead wire, and a tankplaced at the distal electrode TIP. The reason for this has to do withthe unique way that MRI couples into an implanted lead wire system.Because of the distributed inductances in a typical implanted lead wiresystem, the distal TIP is largely decoupled at MRI RF pulsed frequenciesfrom the active implantable medical device itself. In other words, thepulsed RF field from MRI can induce localized loop currents at thedistal TIP while at the same time inducing currents at other locationsin the lead wire system. It is also desirable to prevent high frequencyelectromagnetic interference that is due to the RF pulsed field of MRIfrom entering into the sensitive AIMD circuits. For example, in acardiac pacemaker application, this could cause the pacemaker tomalfunction during the MRI procedure thereby placing the patient's lifein danger. Accordingly, it is a feature of the present invention thatany of the TANK filters 146 as described herein can be placed anywherein the lead wire system, in conjunction with a distal tissue electrode,and/or inside the AIMD itself.

FIG. 47 illustrates a prior art active implantable medical device thatmay or may not incorporate implanted lead wires. This is known in theindustry as a Bion 262. Bions 262 generally come in two differentcategories. That is, certain Bions have an internal battery and are astand-alone stimulation device used for urinary incontinence and otherapplications. These are generally large needle injectable systems. TheBion 262 generally is encased in a ceramic tube 264 that has an end capelectrode 266. The end cap electrode 266, for example, could be titaniumor platinum and is generally welded or brazed to the ceramic tube 264 tomake a hermetic seal thereby protecting the sensitive electronics thatare inside of the ceramic tube 264 from damage due to body fluid. Thereis also an opposite polarity RING electrode 268 as shown. Thisparticular device stimulates body tissue between the cap electrode 266and the RING electrode 268.

Other types of Bions have no battery, but instead have a resonant coil.The device picks up its energy from an externally worn or externallyplaced pulsing magnetic field pack. A patient can wear some sort of adevice around his or her waist or shoulder, for example, with a largebattery and circuit coil that produces this field. The Bion would getits energy by coupling with this field. No matter whether the Bion 262is passive or has an internal battery, it is still important to protectthe internal circuits of the Bion from temporary or permanentmalfunction due to the RF pulse frequency of MRI systems. There are alsocases where the diameter of the Bion 262 is too large for it toeffectively make contact with a precise location within a nerve ormuscle. In this case, the Bion 262 may have an associated lead wire 270with a distal TIP 142. In this case, the end cap 266 and the lead wirewould be insulative wherein the electrical connection to body tissuewould occur at distal TIP 142. A small diameter of lead wire 270 anddistal TIP 142 allows the surgeon to tunnel the lead wire 270 into aprecise location and have the Bion TIP 142 placed at a location withinmuscle, nerve or other body tissue where its location can be precise.However, lead wire 270 can act very much like pacemaker lead wires, inthat it could act as an antenna and pick up undesirable RF fields fromMRI. Accordingly, overheating of lead wire 270, in conjunction with thedistal TIP 142, and/or coupling of electromagnetic interference into thecircuits of the Bion 262 are a concern. Accordingly, it is a feature ofthe present invention that novel TANK filters 146 could be placed inseries with lead wire 270 and/or could be placed internal to the Bion262 as shown in FIG. 48.

Referring to FIG. 48, one can see an application of the presentinvention where inside of the Bion device 262 the parallel TANK circuit146 can be placed at the end cap electrode 266. This would preventselected pulse RF frequencies, for example, those from a 3 Tesla MRIsystem from entering into and disrupting or damaging the sensitiveelectronics of the Bion 262. This placement is the preferred embodimentfor the tank filter because not only will it protect the internalcircuits, but it will also prevent MRI pulsed currents from flowing intothe associated body tissues, or in the case of an external lead wire270, it would prevent RF currents from flowing in that lead wire aswell. Alternatively, the novel TANK circuit 146 of the present inventioncould also be placed at the ground electrode 268. One could also placeresonant parallel TANK circuits at both the cap 266 and the ground 268electrodes. In a preferred embodiment, these could be of differentresonant frequencies. For example, this would make the Bion 262resistant to both 1.5 Tesla and 3 Tesla MRI system which have pulsed RFfrequencies of 64 MHz and 128 MHz respectively. The Bion 262 is just oneexample of an AIMD that may or may not have implanted lead wires. Otherexamples include drug pumps and the like. Accordingly, the presentinvention is very useful to protect the electronic circuits of activemedical devices that do not have associated lead wires, from the highfields involved with certain hospital and other medical diagnosticprocedures such as MRI.

FIG. 49 is a perspective view of an inline Bion 262′. A sinteredtantalum electrode 266′ has a tantalum stem that penetrates an overallglass seal bead 264′. The glass seal bead 264′ protects all of theelectronic components from body fluid intrusion. The Bion 262′ includesa circuit board 272 containing a Schottky diode, wire bond pads andother components for convenient attachment to the embedded copper coils274 and ferrite 276 that are used to couple with the external pulsingmagnetic field. As previously mentioned, the pulsing external magneticfield is how the Bion 262′ is energized. A moisture getter 278 solvesthe problem that body fluid will slowly penetrate through the glass264′. An iridium electrode 268′ is coupled through the glass with atantalum tube 280. The Bion 262′ of FIG. 49 has been modified inaccordance with the features of the present invention to show novel TANKcircuits 146 and 146′. If one wanted the Bion 262′ to be compatible withonly one type of MRI system, then only one novel TANK circuit 146 wouldbe required. For example, the TANK circuit 146 could be designed to beresonant at a 3 Tesla MRI pulsed frequency of 128 MHz. This wouldprevent MRI currents from flowing from the left hand electrode 266′ andthrough the electronics to the right hand electrode 268′ by creating anopen circuit. On the other hand, if one wanted the Bion 262′ to becompatible with two types of MRI fields, then one could include the twoTANK circuits 146 and 146′ as shown in FIG. 49. In this case, the TANKcircuit 146′ would be designed to resonate at a selected MRI frequencydifferent than that of the TANK circuit 146.

FIG. 50 illustrates utilizing the present invention in a multiple TANKseries configuration. One can see that there are three TANK circuits T₁,T₂ and T₃. TANK circuit T₁ consists of a parallel combination of an L₁and a C₁, TANK T₂ consists of a parallel combination of an L₂ and a C₂and TANK T₃ consists of a parallel combination of an L₃ and a C₃. Itwould be desirable to be able to have a patient capable of exposure tonot just one type of MRI system. For example, in a 0.5 Tesla MRI system,the pulsed RF frequency is 21 MHz. One could then desirably design L₁and C₁ to be self-resonant at 21 MHz. 1.5 Tesla MRI systems have a pulseRF frequency of 64 MHz. Accordingly, TANK circuit T₂ could have aparallel inductor and capacitor arrangement consisting of L₂ and C₂ thatwould self-resonate at 64 MHz. The now popular 3 Tesla MRI systems havea pulse RF frequency of 128 MHz. Accordingly, the parallel combinationof L₃ and C₃ could be designed to self-resonate at 128 MHz. This wouldmean that the impedance of the system of FIG. 50, as measured betweenpoints A and B, would be very high at all three of these selected MRI RFpulse frequencies, allowing a patient to be subjected to MRI in any ofthese types of MRI systems without fear of overheating the lead wires ordistal TIP electrode. Another adaptation of the schematic shown in FIG.50 would be, for example, to have one or two of these parallel TANKfilters 146 designed for MRI and perhaps the third TANK filter 146designed to protect the patient against electrocartery surgery. Forexample, Bovi knife surgery operates primarily at one particularfrequency. Thus, it would be possible to design an active implantablemedical device that would be immune to certain types of electrocarterysurgery and also selected MRI frequencies. It will be obvious to thoseskilled in the art that any number of series TANK filters 146 can beconfigured using the novel designs as described herein.

FIG. 51 is an isometric view of the prior art air wound inductor 208shown and described previously. The air wound inductor 208 has multipleturns and is first wound around a mandrel (not shown). The mandrel isthen removed. The structure holds its shape by selecting materials thattake a permanent set as shown.

FIG. 52 is a blow up taken generally from the sectional view 52-52 fromFIG. 51. The blow up view shows a section of the air wound inductor 208.Using a non-ferrous inductor is an advantage in the presence of MRIsignals because the main static field of MRI can cause a ferromagneticcore to saturate. This is not the case for an air wound inductor asillustrated in FIG. 51. The inductor of FIG. 51 will be impervious tothe effect of the static field of MRI because there are no ferromagneticmaterials. In addition, air wound inductors produce very little MRIimage artifact. However, it is important that air wound inductors, suchas those illustrated in FIG. 51, be protected from body fluid. Whenimmersed in body fluid, they will become subject to stray electricalleakage currents from turn to turn. Worse yet, the turn-to-turnparasitic capacitance will change due to the dielectric properties ofthe body fluid itself. Insulating the lead wire 208 will help to reduceor prevent circulating electrical current. However, such insulation willdo little or nothing to reduce the amount of turn-to-turn capacitance.One could postulate that by balancing the turn-to-turn capacitance withthe inductor structure as shown in FIG. 51, one could create the tankcircuit of the present invention. However, there are a number ofpractical reductions to practice problems associated with this. One is,that any change in turn-to-turn spacing (i.e. mechanical manipulation),would effect the capacitance and hence the resonant frequency. Also, itwould be very difficult to test this device in a production situation.Testing such a device in air would not work because the permittivity ordielectric constant of air is 1. Depending on where the inductor wouldbe placed into body fluid (blood, tissue, spinal fluid and the like),will affect the dielectric constant and hence the amount of distributedcapacitance. As stated, if the distributive capacitance varies, theresonant frequency of the tank filter will also vary. One could overcomepart of this difficulty by performing production testing in a saline orgel tank whose dielectric and electrical conductivity properties closelymatch that of the body fluids into which the device is later to beimplanted. This would improve the situation, however, not all patientsare alike. For example, a cardiac patient undergoing difficulties couldhave wide variances in their electrolytes and hence body fluiddielectric properties.

FIG. 53 shows a prior art hollow ferrite core 282 which has a highpermeability. This core contains magnetic dipoles. An optional prior artsolid ferrite or powdered iron core 282′ is shown in FIG. 54. The hollowcore 282 is preferred as it has a larger mean magnetic pathway for theamount of weight and volume of material.

FIG. 55 shows a wire 284 wound around the high permeability ferrite core282. The resulting wound inductor 286 is suitable for insertion withinany of the novel capacitor elements as previously described herein.However, the presence of the ferrite or iron core material can be aproblem in the presence of MRI. The reason for this is that magneticdipoles will align within the static fields of the MRI scanner andsaturate.

FIG. 56 illustrates the ferrite core 282 with additional turns of wire284 in comparison with the wound inductor 286 of FIG. 55.

FIG. 57 is a cross-sectional view taken generally along section 57-57from FIG. 56. As mentioned, using a ferrite core 282 in MRI fields cancause core saturation and image artifacts. However, one could use anon-magnetizing core such as a plastic or phenolic core. Even a ceramicmaterial could be used. In this case, while the amount of availableinductance would be significantly lower, no core saturation or imageartifacts would be realized in the presence of main static field. Itwill be apparent that any of the wound, air wound or core woundinductors, as shown, could also be wound around the outside diameter ofany of the cylindrical capacitor structures as illustrated herein. Thiscould be understood by referring back to FIGS. 35 and 37. The woundinductor 208 could be wound around the outside of the capacitor element168, 184 and then connected to the distal TIP 142. This is lessvolumetrically efficient, but it will increase the length of theinductor and thereby the overall inductance.

FIG. 58 is an isometric drawing of a chip inductor 288 which could beused in place of any of the spiral wound inductors discussed previously.The chip inductor 288 includes a thin substrate 290 which can beceramic, circuit board material or the like. The inductor circuit trace292 includes convenient wire bond pads 294 and 296. This is betterunderstood by looking at the enlarged fragmented view illustrated inFIG. 59. There, an optional wire bond pad 294 a is shown which has beensurface mounted. This provides another way to attach a lead wire, forexample, by gold wire bonding. Also, evident from FIG. 59 is thethickness t of the inductor circuit trace 292. By depositing arelatively thick circuit trace 292, one can minimize the inductor ohmiclosses (series resistance Rs). By minimizing Rs, there is lessattenuation to the desired low frequency biologic signals. For example,in the case of a cardiac pacemaker, biological signals of interest arein the 10 Hz to 1000 Hz frequency range. At these frequencies, theinductive reactance is negligible (approaches zero). However, the seriesresistance R_(s) of the inductor is still present and if too high couldattenuate desired biologic signals. Additionally, the cardiac pacemakeroutput pulse could be attenuated by too much inductor resistive lossthereby presenting an inefficient use of AIMD energy and a potentialproblem for electrical capture (pacing) of the heart. Referring back tothe inductor 286 shown in FIGS. 56 and 57, a major problem with windingmultiple turns of small diameter wire is the relatively high value ofdirect current (DC) resistance that would result. This high resistancewould be undesirable at low frequency in that it could potentiallyattenuate pacing or stimulation pulses and also degrade sensing ofbiologic signals. An additional problem associated with inductors madefrom many turns of fine wire is that they can become their own heatingelement in the presence of MRI. This is also true if the patient wereexposed to an MRI system that was not at the resonant frequency of theTANK circuit. Accordingly, placing a lot of small diameter wire with ahigh series resistance in the implantable device lead wire system isgenerally not a good idea. An aspect of the present invention is thatrelatively small values of inductance are to be used in the TANKcircuits 146. The structure of FIGS. 58 and 59 overcomes suchdisadvantages by providing a volumetrically efficient inductor while atthe same time minimizing the DC resistance.

FIG. 60 is an exploded isometric view taken from area 60-60 in FIG. 59.The only difference is that a small gap 297 has been left between theinductor circuit trace and the termination pad 294A. When this isco-bonded to a ceramic capacitor, this will essentially leave theparallel inductor element mechanically attached but electricallydisconnected from the capacitor element. This is better illustrated inFIG. 61 which shows the capacitor in parallel with the inductor with theinductor electricity disconnected by gap G. For high reliability testingand screening of the TANK circuit, it is very important to be able toelectrically disconnect the capacitor in order to perform highreliability electrical testing and screening of the tank circuit. Highreliability capacitor testing and screening generally consists ofthermal shock, high voltage burn in, and many electrical measurements ofthe capacitor, including capacitance value, insulation resistance,dissipation factor and equivalent series resistance. None of thesemeasurements can be effectively accomplished with the capacitorconnected in parallel with the inductor. Capacitor measurements areusually made at low frequency. If the inductor was placed in parallel,this would tend to short the capacitor out at these frequencies.Therefore, by separating the inductor from the capacitor, it is thenpossible to perform all of these critical high reliability screeningmeasurements. This is important to eliminate infant mortality from thecapacitor lot population. Another advantage of disconnecting theinductor from the capacitor is that it is now also possible to performelectrical tests on the inductor element. As will be seen later, it isimportant that the inductor and capacitor values be selected so thatthey are resonant at the proper frequency. By having them disconnected,it is also possible that their values be selected and adjusted such thatthey will be resonant at precisely the correct frequency. It is alsovery important that high reliability testing be performed at the highestlevel of assembly possible. That is, one would not want subsequentassembly operations to introduce either immediate or latent defects intothe component population. For example, the ceramic capacitors are quitesensitive to thermal shock, wherein cracks or delaminations can beintroduced. It takes extensive electrical screening, including thermalshock and burn in, to detect such defects.

Accordingly, a very small (innocuous) electrical attachment is made tofill the gap to join the capacitor and inductor back into parallel toform the TANK of the present invention. It is very important that thiselectrical connection be done in such a way that it does not thermallyor mechanically stress the capacitor, inductor or electrical connectionelements of the TANK assembly in any way. This is best seen by referringto FIG. 62 which is generally taken from the area 62-62 of FIG. 60. FIG.62 shows a small area of electrical connection material 299. Aspreviously stated, it is critical that the application of electricalmaterial 299 be done is such a way that is simple, and not damaging tothe overall component in any way. Accordingly, an ideal connectionmaterial to fill the gap 299 would consist of the group of a lowtemperature thermal setting conductive polymer, a low energy laser weld,a low temperature braze, a low temperature solder (for non-biocompatibleapplications) or even conductive inks. Any of these can be applied byautomated processes, including robotic dispensing, by screen-printing,stencil or the like. The group of thermal setting conductive adhesivescould include biocompatible adhesives, such as polyimide, silicones, ora number of epoxies and the like.

Referring once again to FIG. 62, the electrical filler material 299 notneed in all cases to be a solid metallurgical bond material. A piece ofconductive rubber, a conductive spring, a metal clip, or conductive fuzzmaterial could be temporarily inserted into the gap 297 so that theresonant frequency of the TANK could be measured (and the TANK tuned).This material could then be easily removed in order to perform theaforementioned high reliability screening test of the capacitor and theinductor element by themselves. This will be more thoroughly describedin the descriptions of how to tune the TANK filter after it is builtwhich will follow in the descriptions of FIG. 119 through 123. After theaforementioned tuning of the TANK is accomplished, then the temporaryelectrical connection clip could be removed and the capacitor highreliability screening could be accomplished. At the very end, after allthe high reliability testing is done, then the permanent (innocuous)electrical connection 299 could be placed as shown in FIG. 62.

FIG. 63 is an exploded view illustrating a methodology of assembling thenovel distal TIP TANK filter 146 of the present invention, which isadaptable to a number of the TANK filter designs described previously,including the single layer tubular capacitor, the multilayer tubularcapacitor and the feedthrough capacitors of FIGS. 35, 37 and 42.

Referring once again to FIG. 63, one can see that there is a woundinductor 286 having a ferrite core 282. This allows the use ofrelatively few turns of large wire due to the high permeability core. Asmentioned, however, it is a problem in an MRI field in that the core maysaturate. The inductor 286 is inserted into a nickel sleeve 298 whichprovides shielding against the main static field of the MRI thuspreventing inductor core saturation. A negative to this approach is thata very large MRI image artifact would result. In terms of manufacturing,it is desired to pre-assemble the novel nickel sleeve 298 to the distalTIP 142. As shown in FIG. 64, the nickel sleeve 298 is laser welded 300to the distal TIP 142. All of this pre-assembly is inserted in anoptional insulation washer 302 which consists of a medical grade plasticmaterial which is biocompatible. A single wall extruded tubularcapacitor 168 is then slipped onto this assembly. A second insulativeplastic washer 304 is then placed onto the tubular capacitor 168. Thecapacitor 168 is placed over the pre-assembly of the nickel sleeve 298and distal TIP 142. The inductor 286 is then inserted inside of thenickel sleeve 298. All of this is best illustrated in thecross-sectional view shown in FIG. 65.

Referring to FIG. 65, there is a hole through the distal TIP 142 whichallows for a laser weld 306 which connects the end of the inductor wire284 to the distal TIP 142. The inductor structure 286 is housed withinthe optional novel nickel sleeve 298 to prevent it from saturating inthe presence of the MRI main static field. To provide additionalshielding against the main static field, the end cap 308 could be a goldplated nickel and nickel could even be incorporated as a part of thedistal TIP 142. This provides complete shielding of the ferrite core 282of the inductor 286. Accordingly, the inductor core 282 is preventedfrom saturating in the presence of the MRI static field. As previouslymentioned, a trade off is that there would be relatively large MRI imageartifact from the presence of the nickel and high permeability corematerial (accordingly, this is not a preferred embodiment). Anelectrical connection 310 is made between the nickel sleeve 298 and theinside diameter metallization 174 of the capacitor 168. At the distalTIP 142, one can see a cross-section of the laser weld 300 that waspreviously accomplished in the pre-assembly shown in FIG. 64.

Referring once again to FIG. 65, the end cap 308 has been gold brazed orotherwise electrically attached 312 to the outside diametermetallization 172 of the tubular feedthrough capacitor 168. To avoid ashort circuit, insulative washer 304 is required to space the conductivecap 308 away from the nickel sleeve 298. Referring once again to the endcap 308, one can see that the inductor lead wire 284 has been routedthrough the end cap in position to abut lead wire 180 that comes fromthe active implantable medical device. For example, the lead wire 180could be part of the bipolar lead wire from a cardiac pacemaker. In thiscase, this would be the lead wire to connect to the TIP 142 (fixationclips not shown) which will contact myocardial tissue. Laser weld orgold braze 314 is used to make an electrical connection to the lead wire180, the inductive wire 284 and the end cap 308 simultaneously.Referring now to the other end of the parallel TANK structure, one cansee the high surface area TIP 142 which is used to stimulate myocardialtissue. Such distal TIPs are well known in the art and can have avariety of shapes and coatings. Distal TIPs that are capable of elutingdrugs are used to prevent tissue inflammation are also available to thepresent invention. Optional insulative washer 302 is shown to preventthe distal TIP 142 from shorting to the capacitor outside diametermetallization 172. It should be noted that for AIMD applications, it isrequired that all of the materials be biocompatible. With specificreference to the nickel sleeve 298, it is noted that nickel in and ofitself is not considered a biocompatible material. Accordingly, a goldplating or equivalent biocompatible coating material is required forAIMD applications. Certain plated iron-containing material or highpermeability nano-materials could be substituted.

A schematic diagram for the novel TANK filter 146 of FIGS. 63-65 isshown in FIG. 66. As previously described, the values of L (286) and C(168) are carefully selected in accordance with the FIG. 12 equation sothat the resonant frequency of the filter 146 that occurs at a selectedRF pulse frequency of an MRI or other electronic system that produceshigh power fields at a specific frequency.

FIG. 67 is an enlarged fragmented sectional view taken generally of area67-67 from FIG. 65. One can see that the optional insulative washer 302has been removed. This is made possible because the external diametermetallization 172 of the tubular capacitor 168 has been held back asshown in area 316. In other words, this unmetallized portion preventsthe distal TIP 142 from shorting to the capacitor outside diametermetallization 172. So, as one can see, there are two ways to accomplishthis: by the insulating washer 302 as shown in FIG. 65, or by selectivemetallization as shown in FIG. 67.

While FIGS. 63, 64, 65 and 67 show an optional nickel shield 298 thatwould prevent a high permeability core 282 of the inductor 286 fromsaturating, there is another way of accomplishing this more efficiently.Referring to FIG. 37, there is illustrated a multilayer tubularcapacitor 184. It is known in the art that nickel electrodes may beused. This is also known as a base metal electrode. Nickel electrodeshave become quite common in commercial applications due to relativelylow cost. Conventional monolithic ceramic capacitors had electrodes madefrom silver, palladium silver, platinum and the like. By constructingthe multilayer tubular capacitor 184 of the present invention asdescribed in FIG. 37 with nickel electrodes, the electrodes themselveswould then shield the inductor 208 from the main static field of an MRIsystem. It is a feature of the present invention that nickel capacitorelectrodes can be used in combination with any of the embodiments hereinto provide degrees of shielding to the embedded inductor. It will beobvious to those skilled in the art that gold plated nickel end caps ortheir equivalent could also be added to the novel multilayer tubularcapacitor 184 shown in FIG. 37 to add additional shielding against themain static field from MRI. As previously mentioned, too much highpermeability material can distort the MRI signals and create seriousproblems with image artifacts. Accordingly, in the preferred embodiment,the electrodes will not be nickel and the inductor will be an air woundinductor. This will make the distal TIP impervious to MRI inducedheating and also will eliminate any image artifact issues.

The present invention also embraces an inductive element 318 which iscompletely embedded within a novel tubular ceramic capacitor structure320. FIG. 68 is a perspective schematic view of such structure, which isparticularly adaptable to prior art multilayer tubular capacitor 184manufacturing techniques as previously described in FIG. 31. Suchcapacitors are generally made by screen printing electrodes while thegreen dielectric is laid flat. After electrode laydown, the capacitor isthen rolled up into the desired tubular shape. The novel tubularcapacitor 320 will include the inductor element spiral 318 as anembedded component. Before the capacitor is rolled up, the inductortrace is laid down on the unfired ceramic wafer by screen printing adiagonal line at a selected layer such that when its rolled up it formsthe spiral as illustrated in FIG. 68.

FIG. 69 is a schematic cross-sectional view generally taken along line69-69 from FIG. 68. This clearly illustrates that the inductor element318 has been embedded within the capacitor dielectric material 322.

FIG. 70 is a more detailed cross-section of the hybrid capacitor 320with an embedded inductor element 318 generally described in connectionwith FIGS. 68 and 69. The hybrid capacitor 320 includes internalelectrode plates 324 and 326 which are typical of multilayer tubularcapacitors such as those shown in FIGS. 31 and 37. Also shown are thetop and bottom metallization layers 328 and 330. The embedded inductorelement 318 spiral winds from top to bottom of the capacitor 320.Because the inductive element 318 is screen printed and fired within thehigh dielectric constant material 322, this will increase theturn-to-turn parasitic capacitance. This capacitance is actuallydesirable as it will add to the amount of capacitance available in theparallel TANK circuit 146. This is better understood by referring toFIG. 71 where it is seen that the inductor element L (318) has a numberof parasitic capacitive elements C₁ through C_(n) shown in parallel withit. The total parasitic capacitance of the inductor is designated C_(L).This capacitance C_(L) ends up in parallel with the main TANK circuitcapacitor C (320) and tends to increase its capacitance value.C_(TOTAL)=C+C_(L). Accordingly, this aids in the overall volumetricefficiency of the parallel TANK circuit 146.

FIG. 72 illustrates an alternative hybrid capacitor 320′ which is verysimilar to FIG. 70. One can see that there are parallel embedded spiralwound inductors L₁ (318) and L₂ (318′). L₁ (318) is near the outsidediameter of the tubular capacitor C (320′) and L₂ (318′) is near theinside diameter of the capacitor. The reason this embodiment is shown isthat in order that the capacitor not delaminate, the inductor traces L₁and L₂ must be deposited relatively thin in a manner similar to thecapacitor electrodes 324 and 326. During firing, this allows good graingrowth of the ceramic and makes for a rugged monolithic structure.However, a negative of using very thin traces for the inductor pattern Lis that this will tend to increase the DC resistance. A way to overcomethis is to use parallel traces L₁ and L₂ (or even n traces) asillustrated in FIG. 72. Of course, using parallel structures puts theinductance from inductor spiral L₁ and L₂ in parallel. This reduces thatoverall inductance by the parallel inductance formula. However, thisdoes have the added advantage of placing the resistances of the twoinductors in parallel thereby significantly reducing the overall DCresistance of the novel structure.

FIG. 73 illustrates yet another hybrid capacitor 320″ which is againvery similar to FIG. 70. In this case, novel embedded inductor spiralsL₁ (318) and L₂ (318′) have both been placed near the inside diameter.It will be obvious to those skilled in the art that such novel inductorspiral structures could be placed literally anywhere within thecapacitor C (320″). It would be generally undesirable to place theinductor spirals between the electrode plates 324 and 326 because thiswould interfere with the electrostatic field and effective capacitancearea (ECA) that develops between such plates.

FIG. 74 is a cross-section taken along line 74-74 in FIG. 73, where theend view of the two inductor spirals L₁ (318) and L₂ (318′) is shown.Also shown is the top view of the electrode plate set 324. As one cansee, as the capacitor C (320″) is rolled up, the electrode 324 wouldappears as a spiral.

FIG. 75 is a cross-section taken along line 75-75 in FIG. 72. One cansee the top penetration of inductor spirals L₁ (318) and L₂ (318′). Onecan also see the top view of the electrode plate set 324 which appearsas a spiral.

FIG. 76 is a sectional view similar to FIGS. 74 and 75 except that anumber of parallel inductor spirals L₁ through L_(n) are illustrated.These are electrically isolated from each other until they are connectedat the respective end metallization areas and related caps. The overallinductance is given by the equation for L_(total) as shown in FIG. 77.It will be obvious to those skilled in the art that multiple parallelinductor traces could be placed near the capacitor OD or the ID or both.

For non-implant applications, conventional capacitor materials can beused for any of the novel TANK circuit embodiments as described herein.For example, referring to FIGS. 35, 37, 42, 44, 68 and the like, forindustrial, commercial, military and space applications, conventionalcapacitor materials can be used. This is best understood by referringspecifically to FIG. 37. For non-medical implant applications thecapacitor electrode plates 186 and 188 could be of palladium silver,nickel or other low cost commercial electrode materials. In addition,termination surfaces 190 and 192 which make attachment to the capacitorelectrode plates could also be of conventional silver, palladium silveror even commercial plated terminations. In addition, electricalconnections 194 and 216 could be of solder or other non-biocompatiblematerials. Lead wire material 196, for example, could be of conventionalcopper and the inductor 308 could also be of copper or any otherconductive material. However, for active implantable medical deviceapplications, it is important that all of the materials used in theconstruction of the novel TANK filters 146 be of biocompatiblematerials. Referring once again to FIG. 37, in the preferred embodimentfor AIMD applications, the electrode plates 186 and 188 would be of pureplatinum or equivalent noble metal. Metallization layers 190 and 192,for example, could be pure gold or pure platinum. Lead wire 196 could beplatinum, platinum-iridium alloy, tantalum or niobium. The inductor wirematerial 308 could be from MP35, platinum, NITINOL or any of thematerials that were previously mentioned for lead wire 196. Theelectrical connection points 194, 214 and 216 would all be either doneby precious metal brazing or by laser welding.

Reference is made to U.S. Pat. No. 6,985,347, entitled EMI FILTERCAPACITORS DESIGNED FOR DIRECT BODY FLUID EXPOSURE, the contents ofwhich are incorporated herein. This patent goes into much greater detailfor the need for all materials to be biocompatible when the capacitoritself is to be exposed to body fluids. An alternative to this would beto construct the novel TANK circuits herein of non-biocompatiblematerials and enclose them in a completely hermetically sealedstructure. This could be accomplished by glass sealing the entirestructure as, for example, illustrated in FIG. 37. It will also beobvious to those skilled in the art that the entire structure shown inFIG. 37 could be placed in an alumina ceramic housing with gold brazedend caps thereby hermetically sealing the entire structure.

FIG. 78 is an isometric view of a prior art rectangular monolithicceramic capacitor (MLCC) 332. It comprises a main ceramic body 334 andit has termination surfaces 336 and 338 for convenient mounting to acircuit board, lead wires or the like. FIG. 79 is a cross-section of thecapacitor 332 taken generally along line 79-79 in FIG. 78. One can seein the cross-section that there are two overlapping electrode plate sets340 and 342. The overlapping of these electrode plate sets forms theactive area of the capacitor 332. Such capacitors are well known in theart and are literally produced in the hundreds of millions for manycommercial, military and space applications.

FIG. 80 is an isometric view of a novel composite monolithic ceramiccapacitor-parallel resonant TANK (MLCC-T) 344 which forms a TANK filter146 in accordance with the present invention. Viewed externally, one cansee no difference between the MLCC-T 344 of the present invention andprior art MLCC capacitor 332 as shown in FIG. 78. However, the novelMLCC-T 344 has an embedded inductor 346 which is connected in parallelacross the capacitor between its opposite termination surfaces 336 and338.

FIG. 81 illustrates an exploded view of the various layers of the novelMLCC-T TANK filter 344 shown in FIG. 80. The novel MLCC TANK (MLCC-T)344 of the present invention includes an embedded inductor 346. At lowfrequencies, the embedded inductor 346 shorts out the capacitor from oneend to the other. However, at high frequency, this forms a parallel TANKcircuit 146 which is better understood by referring to the schematicdiagram in FIG. 82. Referring once again to FIG. 81, one can see that asthe capacitor stacks up from the top, we have an area of blank coversheets 348 followed by one or more embedded inductor layers 346. Theseinductor meander shapes can have a variety of shapes as furtherillustrated in FIG. 83. The meander shapes illustrated in FIG. 83 areillustrative examples and are not meant to be entirely inclusive. Itwill be obvious to those skilled in the art that there are a variety ofoptional shapes that could also be used. Then there are a number ofother blank interleafs 350 before one gets to the capacitor electrodeplate sets, 340 and 342. One can see the capacitor electrode plate set340 which connects to the left hand termination 336 and one can also seethe capacitor electrode plate set 342 which connects to the right handtermination 338. In FIG. 81, only single electrodes are shown as 340,342. However, it will be obvious to those skilled in the art that anynumber of plates n could be stacked up to form the capacitance valuethat is desired. Then bottom blank cover sheets 352 are added to provideinsulative and mechanical strength to the overall TANK filter MLCC-T344. The meander inductor trace 354 is deposited or silk screened ontoanother layer of the monolithic ceramic TANK. This can be one layer ormany layers as desired. As previously noted, when many inductor layers346 are put in parallel, this tends to reduce the overall inductance,but also desirably reduces the DC resistance of the inductor traces. Theembedded inductor layer 346 is known as a meander because it tends tomeander back and forth as it goes through the MLCC-T 344.

FIG. 83 shows a number of alternate meander shapes 354 that areavailable for the inductor 346. After the inductor layer 346 is added tothe stack as shown in FIG. 81, then one or more blank ceramic coversheets 348 are added. The blank cover sheets provide mechanicalstrength, rigidity and electrical insulation protection to the embeddedinductor and ceramic capacitor electrode layers 340 and 342. In atypical monolithic ceramic capacitor manufacturing operation, theaforementioned stack up, as illustrated in FIG. 81, could be done bothby wet-stack processing wherein each ceramic layer is sprayed down as aliquid or in a waterfall process, then pre-dried, and then theelectrical layers (other capacitor electrodes or inductor traces) arelaid down and dried. In a typical ceramic capacitor thick film process,these layers are laid down in ceramic tape and then stacked and pressed.In either case, a monolithic structure is formed which is then stackedand pressed. The methodology that is illustrated in FIGS. 80 through 83inclusive is also applicable to a wide range of other types of capacitortechnologies including tantalum, electrolytic and film. For example,film capacitors can be stacked like an MLCC or rolled encompassing anyof the embedded inductor traces as illustrated herein. Referring back toFIG. 68 through 77 inclusive, one can also see that wound filmcapacitors could also be constructed with an embedded inductor in asimilar fashion. Accordingly, the concepts of the present invention areapplicable to a wide variety of equivalent capacitor technologies. Atthis point, there is a binder burn-out process which raises the green(unfired) capacitor from relatively low temperature to an elevatedtemperature. This process is to allow volatiles and solvents that wereincluded in the ceramic slurry or tape to volatilize and slowly evolveand dissipate out of the monolithic structure. Eliminating thesevolatiles prior to high temperature firing or sintering is necessary sothat the MLCC-T layers will not delaminate. The next step in thisprocess is to fire or sinter the composite MLCC-T 344 at very hightemperature. This causes the ceramic grains to sinter forming a hardmonolithic structure. The last step, referring to FIG. 80, is theapplication of the termination surfaces 336 and 338. These terminationsurfaces can be a thick film ink, such as palladium silver, a goldplating, or the like and applied in many processes that are known in theart. Once again, the overall MLCC-T 344, which is illustrated in FIG.80, looks identical to a prior art MLCC 332. However, embedded within itis the novel inductor structure 346 creating the novel parallel TANKfilter 146 of the present invention.

Again referring to schematic drawing FIG. 82, one can see that theinductor L has been placed in parallel with the capacitor C which is allconveniently located within the monolithic structure MLCC-T 344 shown asFIG. 80.

FIG. 83 illustrates a number of alternate inductor circuit trace layershapes 354 which can be embedded as illustrated in FIG. 81 within thenovel ceramic MLCC-T 344 of FIG. 80. It is desirable not to have theseinductor layers 346 embedded between the capacitor active electrodeplates 340 and 342 which forms the capacitance value C. Placing theinductor(s) 346 between the capacitor electrode plate set 340 andelectrode plate set 342 would tend to interfere with the electric fieldwhich forms the desired capacitive element. This is why in the preferredembodiment, the inductor layers 346 are shown above in the stack-up ofthe blank interleaf sheet area 350 before one gets into the activecapacitor layer.

Referring once again to FIG. 81, in a typical embodiment, one might haveone to five inductor layers 346 (or many more). By putting additionalinductor layers 346 in parallel, one can drop the overall DC resistanceR_(L) which is desirable in an active implantable medical deviceapplication. Referring now to capacitor electrode plate sets 340 and342, these can vary anywhere from two to four plates all the way up toas many as hundreds of alternating parallel plates. The number ofelectrode plates and their overlap area, (along with the dielectricconstant and dielectric thickness) determines the capacitance value fora particular resonant TANK application. Referring once again to FIG. 83,one can see examples of some of the various possible shapes for embeddedmeander inductor elements 346. These will typically be laid down usingbiocompatible materials which will be similar to the same materials usedto form the metallic electrode plate sets 340 and 342. In the preferredembodiment, these would typically be of a noble metal such as pureplatinum or gold which are biocompatible materials. Since these distalTIP TANK filters 146 will be placed in human tissues (for a pacemaker,literally floating in the blood stream). It is very important that allof the materials, including platinum, gold, palladium, tantalum, niobiumand titanium, be biocompatible and extremely reliable. Platinum is anexcellent choice for such biocompatible materials and is preferred inthe novel MLCC-T 344 of the present invention in a process known as ahigh-fire sintering system. Platinum is the preferred embodiment becauseof its excellent compatibility with the ceramic layers such as BariumTitinate, Barium Strontinate, and the like. This is because of the highmelting point of the platinum.

Referring once again to FIG. 83, any of these inductor 346 patterns 354would be laid down by screen printing or equivalent deposition processmethods wherein an inductor meander pattern would be laid down over theblank ceramic material and a squeegee would be passed across which woulddeposit the desired platinum ink pattern 354. Alternative capacitortechnology, for example, stack film capacitors, would generally requirea different methodology of laying down the inductor meander shapesillustrated in FIG. 83. This could include metal plating or depositionon film, flame spraying and the like. It will be obvious to thoseskilled in the art that a number of other possible patterns areavailable. Literally any pattern 354 which forms an inductor 346 andconnects from one end of the capacitor to the other will do the job. Inthis regard, it is very important that the embedded inductor shapes 354that are selected make an electrical contact and connection between theMLCC-T 344 end metallization areas 336 and 338. Referring once again toFIG. 83, there are technical advantages and disadvantages (in noparticular order or preference) of the various inductor meander traces354 shown. Pattern C is a straight deposited trace 354 that runs throughthe MLCC-T 344. This would have very low inductance, but would also havevery low DC resistance. This is because of the fact that the DCresistance is determined by a number of factors. DC resistance is givenby the formula R_(L)=ρL/A wherein ρ is the resistivity of the material,L is the length of the material and A is the cross-sectional area of thematerial which is determined by its deposited thickness and its width.This equation can also be expressed in an alternate form,

$R_{s} = {( \frac{\rho}{t} ){( \frac{l}{w} ).}}$By assuming a standard t for all traces, this expression can be used tocompare series resistances by counting the number of ‘squares’ requiredto create the desired pattern. Accordingly, one can see that the lengthof pattern C is short relative to many of the others, therefore, thiswould have desirably very low DC resistance. However, a disadvantage tothe inductor shown in Pattern C is that it makes for a very inefficientinductor shape. That is, this straight trace would have very lowinductance compared to some of the other shapes in FIG. 83. Pattern Dcomprises three parallel straight inductor paths L₁, L₂ and L₃. Thiswould drop the total inductance in accordance with the parallel inductorequation shown in FIG. 84. Therefore the total inductance of the threetraces 354 in parallel is much less than a single one. However, the DCresistance also desirably drops in parallel just like resistors inparallel. Accordingly, there is a trade off here between the desiredinductance and the amount of DC resistance. Referring to Pattern E, onecan increase the length of the deposited inductor trace 354 by goingfrom one corner to the other forming a diagonal. This increases itslength thereby increasing its inductance while at the same time alsoincreasing its DC resistance which is undesirable. However, aspreviously mentioned, multiple layers can be laid down therebydecreasing the DC resistance. Patterns B and G show alternatemethodologies of greatly increasing the overall length of the depositedinductor circuit trace 354 by making it curved. The advantage of thecurve is that one greatly increases the length of the inductor andtherefore the inductance. Another advantage of curving the meander backand forth is that mutual inductance occurs between the adjacent turns.This also tends to make the overall inductor meander more efficient. Theinductance of the wire or the circuit trace is proportional to itsoverall length and mutual inductance. Curved traces are an efficient wayof increasing the length and the mutual inductance and therebyincreasing the total inductance. Patterns F and I illustrate an evenmore efficient way to increase the overall length and mutual inductanceby a rectangular pattern by wrapping back and forth so that the distancebetween one termination surface 336 and the other termination surface338 is greatly increased. Pattern A illustrates another type of inductorpattern that looks almost like a digital waveform. Pattern J is a veryefficient omega pattern. Another option is shown in Pattern H wherein asaw tooth pattern could be formed. The saw tooth is not very efficientas to mutual inductance. It will be obvious to one skilled in the artthat a number of patterns can be used to increase the length and therebyincrease the inductance. In general, Pattern shapes A, B, F, I and J arepreferred embodiments when compared to the other patterns. This takesinto consideration a balance between the inductance efficiency achievedversus the amount of DC resistance.

Referring once again to FIG. 83 Pattern A, one can see that there is aparasitic capacitance C_(P) that occurs between the adjacent meanders354 of the novel embedded inductor 346. If the inductor trace 354 shapewere in air (dielectric constant=1), this value of C_(P) would berelatively low. However, in the composite MLCC-T 344, the inductor trace354 is embedded within a very high dielectric constant material (such asBarium Titanate with a K of 2000 or greater). Because of this, thedistributed capacitance between adjacent turns of inductor 346 will berelatively high. However, in accordance with the present invention, thiswould serve to add to the total amount of parallel capacitance. This isbest understood by looking at the parallel TANK circuit schematicdiagram illustrated in FIG. 82. The distributed capacitance that wouldoccur in the inductor 346, would add in parallel to the desirablecapacitance C in creating the parallel TANK circuit 146.

In actuality, if one is to carefully design the amount of distributedcapacitance C_(P) as illustrated in FIG. 83, one could totally eliminatethe need for a separate discrete capacitor. Referring back to FIGS. 80and 81, this means that if one were to control the distributivecapacitance of the inductor 346, one could then eliminate the capacitorelectrode layers 340 and 342. This would be a preferred embodiment ofthe present invention wherein the parallel resonant TANK filter 146could be entirely created using the distributive capacitance of theinductor itself.

Referring back to FIG. 51 and looking at the parasitic capacitanceC_(P), one can see that the same principles can be applied to an airwound inductor (or an inductor embedded within any other dielectricmaterial). In an air wound inductor, the distributive capacitance is notas efficient (will not be as high) as for an inductor embedded andco-fired within a high dielectric constant material. However, if therewere a huge number of turns that were closely spaced, it would still bepossible to use the parasitic capacitance as shown in FIG. 51 toresonate with the inductance in such a way that the entire structurebecomes a resonant TANK circuit in accordance with the presentinvention. A major disadvantage of this approach for the presentinvention is that when the air wound inductor is placed into body fluid,it would be in a medium having different dielectric properties than air.This would change the distributed capacitance and thereby the resonantfrequency. Worse yet, the relatively high conductivity of body fluidwould cause turn to turn leakage currents to flow. One practical way touse an open solenoid inductor structure would be to place it into ahermetically sealed package. This would become very large andimpractical for venous insertion and/or tissue tunneling surgicaltechniques. Accordingly, open solenoid inductors resonating with theirown turn to turn parasitic capacitances represent a less desirableapproach.

Referring to FIG. 85, one can see that any of the aforementionedinductor circuit traces 354 from FIG. 83 could also be printed ordeposited right on top of a prior art MLCC capacitor 332 to form MLCC-T344′. In this case, they do not need to be embedded and co-fired withinthe entire ceramic capacitor. The advantage here is that low cost MLCCswhich have been produced from very high volume commercial capacitoroperations could be utilized and the inductor trace 354 could be printedon as a supplemental operation.

FIG. 86 is the schematic diagram of the FIG. 85 novel MLCC-T 344′. Theinductor 354 imprinted onto the capacitor 332 could be made of pureplatinum or pure gold so that it would be biocompatible and suitable fordirect exposure to body fluids. This is a very convenient rectilinear(flat) geometry in that it is readily adaptable to electrodes that aretypically used for neurostimulators, deep brain stimulators, spinal cordstimulators and the like. The previously described coaxial parallel TANKcircuits are more applicable to insertion through veins like thesubclavian vein and down through the valves of the heart for convenientinsertion into the right ventricle for example. Coaxial geometries arealso particularly adapted where the physician must use surgicaltunneling techniques to insert an electrode. For example, tunnelingtechniques are commonly used for neurostimulators to insert a lead wireto stimulate a particular nerve or muscle in a paralyzed patient.

FIG. 87 shows yet another way to deposit any of the inductor shapes 354as previously described in FIG. 83 onto a separate substrate 356. Forexample, this substrate 356, could be of alumina ceramic or othersuitable circuit board material. This could then be bonded with a thinadhesive layer 358 to a prior art MLCC capacitor 332. The compositeMLCC-T structure 344″, including corresponding metallization surfaces336 and 338 on opposite ends, is illustrated in the electrical schematicdiagram of FIG. 88 where it is evident that the structure forms theparallel L and C TANK circuit 146 of the present invention.

FIG. 89 is a sectional view taken along line 89-89 of FIG. 87. FIG. 90illustrates an alternative configuration wherein two inductor layers 354and 354′ are deposited on opposite sides of substrate 356. FIG. 91illustrates a multilayer substrate 356 having an embedded inductor layer354′ along with surface inductor layers 354 and 354′. FIG. 92illustrates a completely embedded multilayer substrate 356 where thereare no inductors on the surface. In this case, inductors 354″ are allembedded within the structure. Referring to FIGS. 89, 90, 91 and 92, allof these inductor substrate structures are designed to be co-bonded tothe ceramic MLCC capacitor 338 as illustrated in FIG. 87.

FIG. 93 is similar to FIG. 28 and illustrates a bipolar pacemaker leadwire system such as that shown in FIG. 10. There are two coaxial leadwires 104 and 104′ that are connected to the RING electrode 144 and thecardiac TIP electrode 142 respectively. These lead wires are routed froman active implantable medical device 100 (not shown). As one can see,the lead wires 104 and 104′ are coiled around each other. In mostcardiac applications, the RING electrode is coaxially wound around theinner TIP electrode lead wire. Referring to TIP lead wire 104′, one cansee that a prior art MLCC chip capacitor 332 has been inserted such thatthe coils of the lead wire 104′ wrap around it. This is best understoodby referring to FIG. 94 which is an enlarged view generally taken ofarea 94-94 of FIG. 93. Such prior art MLCC chip capacitors 332 arewidely available very inexpensively as they are produced in very highvolumes. Electrical connections 360 and 362 connect the lead wire 104′to the capacitor metallization surfaces 336 and 338. This puts the leadwire 104′ in parallel with the capacitive element. The lead wire 104′,due to its coiled geometry, makes a very efficient inductor element. Thecombination of the coiled inductance L and the prior art MLCC yields thenovel parallel resonant TANK filter circuit 146 of the presentinvention, as illustrated in FIG. 95. It will be obvious to thoseskilled in the art that all of the materials used to construct the MLCCchip capacitor 332 and its electrical attachments to the lead wire 104′should be biocompatible. This is because it will be directly exposed toeither body fluids or body tissue. As previously described, it isdesirable for high reliability testing and screening purposes to be ableto do proper burn in and electrical measurements of the TANK capacitorelement 332. As mentioned, this is very difficult to impossible to dowith the inductor L_(coil) connected in parallel with the capacitor 332.Referring back to FIG. 94, one can see, for example, electricalconnection 360 could be left disconnected until the aforementionedcapacitor high reliability screening is accomplished. Then, the smallinnocuous electrical connection 360 could be made. It would have to bevalidated during the manufacturing process that such electricalconnection did not introduce any latent defects into the capacitor lotpopulation. The way to accomplish this would be to snip L_(coil) with apair of cutters, for example, near the section marked a and then go backand do capacitor high reliability screening. This snipping disconnectionwould be destructive of the devices under test. This could be doneduring initial qualification testing on a large sample of parts. Theseparticular parts would never be slated for commercial or human implantapplications. Performing this type of testing on a capacitor elementafter it has been completely built will prove that the electricalconnection 360 did not damage the capacitor in any way. During thisfollow-up high reliability screening, there should be zero failures inthe capacitor lot population.

FIG. 96 is a more detailed schematic drawing of the parallel TANKcircuit 146 of the present invention. One can see that there is aninductor element L and in addition, there is a resistive element R_(L).R_(L) represents the parasitic resistance of the circuit trace 354 orwire used to form the inductor element itself. One can also see that thecapacitor element C has a resistor in series which is known as thecapacitor equivalent series resistance (ESR) or R_(C). Referring onceagain to FIG. 96, the resistance R_(L) shown in series with the inductorand/or the ESR, R_(c) shown in series with a capacitor can be eitherparasitic (a property of the inductor of the capacitor element itself)or they can be added resistances as separate components. For example, ifit were found to be desirable to increase the value of R_(L), one couldadd a small resistor chip or element in series. In the presentinvention, the relationship between the R_(L), R_(C), L and C are veryimportant, and is best understood by understanding how the TANK filter146 works in an actual active implantable medical device application.

Biological signals are very low in frequency. In fact, in a cardiacpacemaker application, all cardiac signals of interest occur from 10 to1000 hertz. However, MRI pulse frequencies tend to be relatively high infrequency. For example, MRI frequencies for a 0.5 Tesla system are 21MHz. This goes all the way up to 128 MHz for a 3 Tesla system. The novelTANK filter 146 of the present invention is designed to be placed inseries with an active implantable medical device lead wire system, forexample, connected between points X and Y (See FIG. 96). For example, inthe case of a cardiac pacemaker, the output pulses from and sensing tothe cardiac pacemaker would be connected at point X, whereas point Ycould be connected to the distal TIP which is the electrode used toconnect to myocardial tissue. Referring again to FIG. 96, it would bevery desirable to have the overall impedance of this TANK filter circuit146 to be very low at biological frequencies. If one considers theformulas in FIG. 15 for capacitive reactance X_(C) and inductivereactance X_(L), one will see that at very low frequency, the capacitortends to look like an open circuit and the inductor tends to appear as ashort circuit. At very high frequencies, such as cell phone or radarfrequencies, the inductive reactance X_(L) is very high (open circuit)and the capacitive reactance X_(C) tends to be very low (short circuit).Therefore, at very low (biologic) frequencies, from 10 to 1000 Hz, therewould be insignificant or zero current that flows through the right handside of the FIG. 96 TANK filter circuit 146 through the capacitorelement C. Accordingly, the ESR (R_(C)) of the capacitor is notimportant at all at biological frequencies. However, referring to theleft side of the schematic shown in FIG. 96, the inductive reactanceX_(L) is quite low when the frequency is low. One can see from the X_(L)equation that as f approaches zero the inductive reactance alsoapproaches zero. In other words, at biological frequencies (below 1kHz), for all practical purposes, the reactance X_(L) of the inductorelement L is zero. Therefore, at low frequency the impedance betweenpoints X and Y is entirely determined by R_(L) which is the resistiveproperty of the inductor. The very low frequency (biological) model ofthe TANK filter circuit 146 is shown in FIG. 97 which consists entirelyof R_(L). At very high frequencies (well above TANK filter circuitresonance), the inductive reactance tends to be very high or almostinfinite. Therefore, at high frequencies well above TANK filterresonance, little to no current flows through the left hand side of theschematic diagram of FIG. 96. As previously discussed, at very highfrequencies, the capacitive reactance X_(C) tends to short circuit.Therefore, at high frequencies, the equivalent circuit model for theTANK filter circuit is shown in FIG. 98 which consists solely of thecapacitor's equivalent series resistance (ESR), R_(C). (Note: thisassumes a high frequency coaxial feedthrough capacitor whose parasiticinductance is small enough to be ignored.)

For an AIMD lead wire application, one really doesn't care about toomuch high frequency attenuation. In addition to blocking and stoppingthe flow of RF currents introduced from MRI radio frequency signals, oneis really only interested in passing low frequency biologic signals bothin sensing and in delivering stimulation signals or pulses to bodytissue. For example, in the case of a cardiac pacemaker, the pacingelectrode which connects into the right ventricle provides low frequencypulses so that the heart can beat properly. At the same time, it is alsosensing cardiac activity in the frequency range from 10 Hz to 1 kHz sothat it can make rate or output threshold adjustments as appropriate.However, one does not really care whether there is a great deal ofimpedance in the lead wire system at high frequencies that are wellabove the resonant frequency of the TANK filter. In fact, a high leadwire impedance is desirable to attenuate undesirable electromagneticinterference (EMI), such as from cellular phones, etc. Accordingly,referring back to FIG. 96, when considering EMI, one does not reallycare how high the ESR (R_(C)) of the capacitor goes (the capacitor couldalso have relatively high internal inductance). In fact, it is desirablethat this ESR value be relatively high. It is also desirable that thevalue of R_(L) which is the resistance of the inductor be as low aspossible. Keeping R_(L) low prevents attenuation of desirablestimulation pulses (minimizing energy loss to the battery of the AIMD).Keeping R_(L) quite low also prevents attenuating low frequencybiological signals so they may be properly sensed by the AIMD. However,when considering the band pass filter characteristics and the impedanceof the TANK filter at its resonant frequency, the situation is not assimple as described above. It is desirable to have some seriesresistance in the inductor and capacitor elements so that the bandwidthof the tank will not be too narrow at the resonant frequency. If thebandwidth is too narrow, it will literally be impossible to build thetank filter due to the practical tolerances of the components used.However, adding too much resistance to the inductor or the capacitorside of the TANK circuit will decrease the overall Q so much that theattenuation of the resonant TANK filter is reduced or even that itsfrequency of resonance has been shifted. This has the effect of reducingthe impedance of the TANK filter at its resonant frequency and therebyundesirably reducing its attenuation to the MRI pulsed frequencies.Accordingly, a careful balance must be achieved between all of thesefactors to create sufficient impedance of the resonant TANK filter suchthat it prevents overheating of implanted lead wires and theirassociated electrodes.

Referring back to FIG. 24, one can see a family of curves whichillustrates the resonance and the TANK characteristics of the novel TANKfilter circuit 146 of the present invention. Curve trace 166 indicatesthe use of a very high Q capacitor and a very high Q inductor. Thiswould mean that the resistive loss R_(L) of the inductor and theresistive loss R_(C) of the capacitor would both be very low. This leadsto a very high Q TANK filter circuit which has a very narrow resonantdip and a correspondingly very high attenuation (or impedance Z) asshown. This is indicated by the relative close spacing of points a and b(3 dB down points) on curve 166.

It is a feature of the present invention to use a relatively high Qinductor which means that its resistive loss R_(L) would be very low incombination with a relatively lossy low Q capacitor element C. Thismeans that the capacitor element would have an ESR or resistive lossR_(C) that would be relatively high. This would result in a medium Qresonant TANK circuit shown as curve 164 in FIG. 24. As previouslystated, this allows biological signals to pass through the TANK filterwith little to no attenuation. However, at high frequencies a great dealof attenuation would be presented both at the MRI pulsed frequencies andat even higher frequencies (such as cellular telephones). This has thedesirable effect of broadening the bandwidth of the TANK filter. This isvery important in that this makes it possible to attenuate the RF pulsedfrequencies from multiple types of MRI systems. For example, the olderstyle 0.5 Tesla MRI frequencies embody RF pulsed frequencies at 21 MHz.A very common MRI system that operates at 1.5 Tesla has a MRI pulsedfrequency of 64 MHz. Newer MRI systems tend to operate at 3 Tesla andabove and have MRI pulsed frequencies that range from 128 MHz all theway to 213 MHz (and even higher). Accordingly, by carefully controllingthe inductor and the capacitor quality factors (Q), one can broaden theTANK filter resonant characteristic such that the novel parallel TANKfilter circuit 146 of the present invention effectively blocks the RFpulsed frequencies from a wide variety of types of MRI systems and otheremitters. Referring back to FIG. 24, one can go too far with thisapproach as shown in curve 162. This would be a situation where the Q ofthe overall TANK filter circuit is so low that it no longer offersenough attenuation at any frequency. Accordingly, a careful balance isdesired between the component losses of the L and C elements and theTANK resonant bandwidth of the parallel TANK filter circuit. Modelingusing P-Spice in correlation with actual prototype measurements hasshown that the following set of values works well for the resonant TANKof the present invention: this includes be a capacitor value of 41.3 pf,a capacitor equivalent series resistance of 10 ohms, an inductance valueof 150 nanohenries, and an inductor resistance of 1.0 ohms. Thiscombination yields an impedance of greater than 50 ohms at the resonantfrequency while keeping the bandwidth wide enough to make the devicerelatively easy to manufacturer and calibrate.

There is another reason that it is very important to broaden the widthof the TANK filter characteristic of the present invention. This has todo with the practical limitations of component tolerances. In a veryhigh Q TANK filter it would be very difficult to manufacture theinductor and parallel capacitor such that they resonated at the correctfrequency. For example, in a 64 MHz MRI system it would be necessary tobuild a very high Q capacitor-inductor TANK with capacitance andinductor tolerances at less than +/−0.1%. In terms of practicalcomponent manufacturing this would be very complicated, very costly andvery difficult. Laser trimming methods would be required to tune thesecomponents to the precise frequency. An added problem would occur overtime. That is, most capacitor dielectrics tend to age which means theylose capacitance over time. Accordingly, even though one precisely tunedthe components so that they would be resonant at the correct frequency,over the life of a typical active implantable medical device acapacitance value would drop over time which would shift the resonantfrequency of the TANK. This means that the resonant frequency of theTANK could shift in such a way that it was no longer effective at theMRI RF pulsed frequency. In other words one might start with a resonantcircuit precisely tuned at 64 MHz, but after five years in a humanimplant application this resonant frequency could shift to 50 MHz whichwould mean that the TANK filter would no longer be effective. This agingconcept and bandwidth control are more completely described inapplication Ser. No. 60/767,484 entitled LOW LOSS BAND PASS FILTER FORRF DISTANCE TELEMETRY PIN ANTENNAS OF ACTIVE IMPLANTABLE MEDICALDEVICES, the contents of which are incorporated herein.

FIG. 99 illustrates one illustrative geometry (form factor) for a priorart MLCC capacitor 332 wherein the length (l) to width (w) ratio betweenthe electrodes 340 and 342 (FIGS. 100 and 101) forms a capacitor thatwill inherently have very low ESR (R_(C)). The reason the ESR of theelectrodes shown in FIGS. 100 and 101 is quite low is that they are verywide W compared to their length L (Ref. the basic resistance formulaR=ρL/A, where: ρ=resistivity; L=length of electrode; and, A=area ofelectrode (width times thickness) in that we have minimized the lengthand maximized the cross-sectional area by maximizing the width.

The relationship between capacitor equivalent series resistance andcapacitor dissipation factor and electrode plate loss is best describedin a (ESR) technical paper entitled, DISSIPATION FACTOR TESTING ISINADEQUATE FOR MEDICAL IMPLANT EMI FILTERS AND OTHER HIGH FREQUENCY MLCCAPACITOR APPLICATIONS. This paper was authored by Bob Stevenson(co-inventor) and was given at the 2003 Capacitor and ResistorTechnology Symposium Mar. 31-Apr. 3, 2003 in Scottsdale, Ariz. Alsocited is a technical paper entitled, A CAPACITOR'S INDUCTANCE, given atthe 1999 Capacitor and Resistor Technology Symposium (CARTS—Europe),Lisbon, Portugal Oct. 19-22, 1999.

FIG. 102 illustrates an alternative geometric embodiment (form factorreversed) for the prior art MLCC capacitor 332″ in comparison to thatshown in FIG. 99. In this case, the width (w) to length (l) ratios havebeen reversed. The electrodes 340 and 342 (FIGS. 103 and 104) are nowquite long compared to their width. This will tend to increase theirresistance (R_(C)). As previously stated, in certain designs to controlthe Q of the TANK, the present invention, it is actually desirable toincrease the ESR of the MLCC capacitor 332″. This has to do with the Qof the parallel resonant TANK filter circuit 146 and corresponding(relative) bandwidth. As previously discussed, the parallel TANK circuitis resonant at one particular frequency. This forms a notch (TANK) inthe frequency attenuation characteristic. However, by increasing thecapacitor ESR, which decreases the Q of the TANK filter circuit, one canwiden this notch. This is important, for example, in the case of aparallel TANK filter circuit designed to reduce the heating in an MRIsystem. For example, in the case of a 3 Tesla MRI system which wouldhave an RF pulse frequency of 128 MHz, one would design the parallelinductor and capacitor to be resonant at 128 MHz. The parallel TANKfilter circuit 146 will look like an open circuit or infinite impedanceat this one frequency only. However, it is relatively difficult tomanufacture the ceramic capacitor and the parallel inductance to beprecise enough to always resonate at precisely 128 MHz. In addition,MLCCs capacitors age over time. A typical MLCC capacitor will lose 2% ofits capacitance for each decade of time. For example, at 1000 hours, ifa ceramic capacitor had 1000 picofarads, the next decade of aging wouldoccur at 10,000 hours whereas its capacitance value would drop by 2%(drop to 980 picofarads at the end of this 10,000 life period). Thiswould mean that it would no longer be perfectly resonant at 128 MHz.However, by reducing the Q of the overall system, one can broaden thebandwidth so that it does not really matter. By controlling capacitorESR, the effective bandwidth of the TANK filter 146 could be increasedso that it would be resonant anywhere from, for example, 20 MHz all theway up to 213 MHz thereby accounting for tolerance variations in thecapacitor and the inductor and their aging characteristics. This wouldalso allow for attenuation of several types of MRI systems with a singleL-C parallel TANK filter (MLCC-T). For example, the RF pulsedfrequencies of 0.5, 1.5 and 3 Tesla MRI systems are 21, 64 and 128 MHzrespectively. The MLCC-T TANK of the present invention could be designedwith high enough capacitor ESR to adequately attenuate two of these MRIpulse frequencies to eliminate concerns due to lead wire or distal TIPoverheating. Referring to FIG. 96, the capacitor's ESR (R_(C)) couldalso be supplemented (or replaced) by an additional or discrete resistorelement, however, for volumetric efficiency (and cost and reliability),the preferred embodiment is to adjust the capacitor's ESR. Accordingly,it is a desirable feature in the present invention to reduce the Q ofthe capacitor thereby increasing the bandwidth of the parallel resonantTANK filter circuit 146. Also, the Q of the overall resonant L-C TANKfilter can be controlled by increasing the series resistance of theinductor as well. However, there is a limit to this because at lowfrequencies, all of the desirable biological currents flow through theinductor. Therefore, one does not want to increase the resistance of theinductor too much because the desirable biological frequencies and evenpacing pulses could be attenuated significantly. Therefore, increasingits resistance L_(R) too much to affect the Q would be a highlydetrimental thing to do because it would end up undesirably attenuatingpacing pulses, and also undesirably degrade or attenuate biological orneurological activity that is used for sensing and adjusting the activeimplantable medical device. Accordingly, it is a feature of the presentinvention to adjust the ESR (R_(C)) of the capacitor and inductorelements in a balanced way such that the bandwidth of the parallel TANK,TANK filter is broadened at the resonant frequency in such a way thatthe bandwidth is wide enough and the impedance at resonance issufficient to reduce of eliminate lead wire and distal TIP heating.

FIG. 105 shows a novel method whereby one can further increase theequivalent series resistance (R_(C)) of the capacitor electrodes. Thisis done during manufacturing by depositing very thin electrodes 340and/or putting dots in the electrode silk-screen pattern such that holes364 appear in the deposited electrode. It will be obvious to thoseskilled in the art that these holes 364 can have any shape from oval tosquare to rectangular. By depositing very thin electrodes 340 and/oradding holes in the electrode, one can decrease the cross-sectional areaof the electrode thereby increasing its equivalent series resistance.Remarkably, experiments have shown that this has little to no effect onthe capacitance value itself since the electrostatic field forms a spacecharge across these holes.

FIG. 106 illustrates an alternative way of depositing holes 364′ ofvarious diameters which can even out the capacitor electrode's 340electrostatic field even further, while at the same time, increasingESR. It should be noted that the total capacitor losses include lossesdue to dielectric loss tangent, capacitor electrode plate losses,capacitor termination or connection losses, skin effect and the like.However, for the purposes described herein, the self-resonant frequencyof modern MRI systems occurs at frequencies that are generally above 10MHz. At frequencies above 10 MHz, the capacitor's dielectric losses(dielectric loss tangent) approaches zero. Accordingly, dielectriclosses can be safely ignored in the present invention. This is morethoroughly described in U.S. Pat. No. 6,765,779. In addition, since theMLCC-T structure 344 contemplated herein is very small, skin effect canalso be ignored. Skin effect usually becomes an important phenomenon atfrequencies above 500 MHz. In addition, the capacitor's insulationresistance, which would be a resistor appearing in parallel across thecapacitor, can also be ignored. This is because modern capacitormanufacturing technology guarantees that the value of this insulationresistance be greater than 10 megohms. Ten million ohms is so largecompared to the reactance values of the other components in the circuitthat the insulation resistance can be completely ignored. In addition,the capacitor's termination and contacts to those terminations arerobust and highly reliable. Accordingly, the resistance of thoseconnections is trivially small. What all of this amounts to is that theonly resistance that is really critical in the present invention is theresistance of the electrode plates 340, 342 themselves. In other words,by controlling the high frequency resistance of the electrode plates, wecan control the Q of the capacitor at its resonant frequency and therebycontrol the bandwidth of the parallel resonant TANK filter 146. Otherways of controlling the capacitor ESR or R_(C) include using a discreteresistor element in series with the capacitor element. There are avariety of prior art resistor chips and the like that are known. Onecould also use electrical attachment materials to the capacitor that arerelatively high in resistivity. Another approach would be to usecapacitor dielectrics that have a particularly high dielectric losstangent within the band of the MRI pulsed frequencies. High frequencydielectric loss tangent presents a resistive loss which would broadenthe TANK filter characteristic (reduce its Q). In a preferredembodiment, the most efficient way to control capacitor ESR (R_(C)) isto increase the resistivity of the electrodes themselves. This resultsin the most efficient packaging. However, all of the aforementioned andother methods can be used. One can also make Q adjustments by addingsome series resistance to the inductor. This is relatively easy to dosince all inductors have some parasitic series resistance. By making aninductor trace 346 thinner, one can increase the inductor resistance.However, this can only be done slightly as one does not want toundesirably attenuate biologic signals or pacing pulses. The designermakes a careful balance between the inductor Q and the capacitor Q inorder to achieve the desired (wide enough) TANK characteristic.

FIG. 107 illustrates an MLCC-T 366 utilizing custom or commerciallyavailable inductor chips 368 and 370 to form the structure as shown.Commercial inductor chips are commonly available at very low cost. Forexample, Murata part no. LQP15MN2N7B02D is a 2.7 nanohenry inductor chipwhich has a Q of 13 and a very low DC resistance of 0.3 ohms maximum.These are available at the 100-piece quantity for only $0.16 each(sixteen cents). These are available in a wide range of inductancevalues and DC resistance Q values. Another is Murata part no.LQP03TLQP03T, which is a 2.7 nanofarad +/−2 nanofarads with a DCresistance of only 0.21 ohms.

A drawback to using commercial off-the-shelf inductor chips 368, 370 hasto do with the fact that they typically contain ferro-magneticmaterials. In an MRI system this is not preferable because anyferro-magnetic materials will produce what is known as image artifacts.This distorts the MRI image in the immediate area of the implant ofdistal TIP which is undesirable. In the preferred embodiments of thepresent invention, all inductors are perfectly composed of either airwound or circuit traced deposited inductor spirals or meanders such thatno ferro-magnetic materials are utilized.

It is interesting to note that some experimenters in attempting todesign filters for MRI applications have made the mistake of using theMRI RF birdcage coils only. That is, an MRI system with RF field coilswithout the presence of the main static field (B₀). One of the mainexpenses in installing an MRI system is related to the cost of the superconducting coils and associated cryogenics that generate the powerfulstatic magnetic field. Accordingly, many investigators save a great dealof expense by installing what, from the outside, looks identical to anMRI system. For example, you would see the toroid shape into which thepatient would normally be inserted. However, missing are all thecryogenics and the apparatus necessary to generate the main staticfield. This can lead one to erroneous conclusions because the staticfield can greatly affect the performance of electronic componentsparticularly if they contain even trace amounts of ferrite or ferrousmaterials. In all of the preferred embodiments of the novel TANK filterinvention herein, the inductor element and the capacitor element isconstructed entirely of non-ferrous materials. Another advantage of thisapproach is that this will have little to no image artifact problems.Image artifact is a very important issue. It is a goal of the presentinvention to protect the lead wires of an implantable medical device tothe extent that it would be possible to directly image (take MRI slicesthrough) the area of the lead wires or even the distal electrodeinterface. For example, in a cardiac pacemaker application, this wouldallow for precise MRI imaging of the right ventricle which is preciselywhere, for example, the cardiac distal TIP would be placed. If thiscardiac distal TIP created a large image artifact, then the MRI imageslices that would, for example, be looking at ventricular wall motionwould become useless. Accordingly, it is a very important feature of thepresent invention that not only does the TANK filter have to protect thelead wires and the distal TIP from overheating, but it also has almostno image artifact. Accordingly, when we refer herein to inductor chips,we are talking about specialty inductor chips that do not involve anyinternal ferrite material.

Referring back to FIG. 87, one can see that any commercially off theshelf inductor chip 368, 370 could be substituted in place of thesubstrate 356. Now back to FIG. 107, one can see that two or more ofthese chips 368, 370 can be used in the novel configuration shown, whichis better understood by referring to the electrode sets shown in FIGS.104 and 105. The FIG. 108 electrodes 372 come out to metallization band374. It is the overlap of the FIG. 108 electrodes 372 with the FIG. 109electrodes 376, 378 which forms the novel series capacitor elements.This gives us two capacitor elements in series that is better understoodby referring to the schematic in FIG. 110. Inductors 368 and 370 areattached mechanically and electrically as shown in FIG. 107, which formstwo series parallel TANKs F_(R1) and F_(R2) as shown in FIG. 110. Byadjusting the values of the capacitors C₁ and C₂ relative to theinductors L₁ (368) and L₂ (370), one can have the two TANKs F_(R1) andF_(R2) resonate at 2 different frequencies. For example, F_(R1) might beresonant at 64 MHz, which is the pulsed frequency of a 1.5 Tesla MRIsystem. F_(R2) could be designed to resonate at 128 MHz, which is thepulsed RF frequency for a 3 Tesla system. In this way, the structureshown in FIG. 107 would make the active implantable medical device leadwire system compatible with both 1.5 Tesla and 3 Tesla MRI systems. Thiswould broaden the patient indication, which is desirable.

FIG. 111 shows yet another alternative embodiment MLCC-T 366′ where asingle inductor chip L₁ (368) could be placed across a specially formedMLCC chip 332. This is better understood by referring to the novelelectrodes 372′ and 376′ shown in FIGS. 112 and 113. The compositestructure forms a parallel TANK filter 146 of the present invention asshown in the schematic of FIG. 114.

FIG. 115 is a prior art unipolar coaxial capacitor 220 (feedthrough)with an inductor 380 deposited, attached, printed on, or embedded withinit. The spiral inductor 380 can be placed by any of the previouslydiscussed methods, including embedding it and co-firing it within theceramic capacitor 220 structure, by printing it directly on top of thecapacitor, or by printing it on a substrate and then co-bonding it tothe capacitor. All of these techniques have been previously described.Inductor spirals are very efficient. Using modified Wheeler equationsone can predict the inductance of such spirals. Because of their extremeefficiency due to the mutual inductance, the inductor spiral is thepreferred embodiment of this invention.

FIG. 116 is the schematic diagram showing the parallel inductor andcapacitor of FIG. 115. FIG. 117 is a sectional view taken along line117-117 of FIG. 115, showing how one could put this in series anywherein the lead wire 238 system of an AIMD.

FIG. 118 illustrate a structure that is very similar to FIG. 115 in thatit is a feedthrough capacitor 220′. However, in this case, it is square.It will be obvious to those skilled in the art that this could be anyfeedthrough capacitor geometries including multi-hole, planar arraydevices.

Referring once again to prior art FIG. 2, one can see that there istypically an unfiltered RF telemetry pin 116 as shown. The RF telemetrypin is designed to pick up a very narrow band of discrete frequenciesthat are used to interrogate, reprogram or recover stored waveforms fromthe implanted device. It is not possible to use prior art low pass EMIfilters (feedthrough capacitor type) on the RF telemetry pin becausesuch filters would also undesirably eliminate the RF telemetryfrequency. However, the presence of this unfiltered antenna 116 canpresent a very serious problem in the presence of very high power EMIfields. Once an EMI field has entered the inside of the housing 102 ofthe implantable medical device, it can cross couple and/or reradiate toadjacent circuits. These inappropriate EMI signals could be sensed bythe cardiac pacemaker, for example, as a dangerous or inappropriateventricular arrhythmia. Worse yet, in a pacemaker dependent patient,such cardiac signals can be interpreted as a normal heart beat whichwould cause the pacemaker to automatically inhibit (a life threateningsituation for a pacer dependent patient). One of the most powerful RFfields that an implantable device patient will ever encounter is insidethe bore of a typical MRI device. Accordingly, there is a need toprotect the RF pin antenna 116. The tank filters of the presentinvention are ideal for this.

Referring once again to FIGS. 115 and 118, one can see two idealexamples of where tank filters could be placed immediately adjacent tothe telemetry pin. This would be most easily accomplished by placing thetank filter of the present invention on the RF telemetry pin 116 on theinside of the AIMD housing. This way the tank filter would be protectedfrom body fluids. In this case, the Q of the inductor and the capacitorused to form the tank filter should both be relatively high. This isbecause we want the 3 dB bandwidth to be relatively narrow. The reasonfor this has to do with the frequencies of interest. For example, for a3 Tesla MRI system, the RF pulse frequency is at 128 MHz. The lowestcommon telemetry frequency is at 402 MHz. Therefore, it is veryimportant that the tank filter response curve drop off very rapidly sothat the desired telemetry frequency not be unduly attenuated. Anotherway around this is, for example, to design the tank filter to beresonant at 64 MHz and restrict the patient to only 1.5 Tesla MRIs. Yetanother way to get around this is to increase the telemetry frequency.Telemetry frequencies in the 850 MHz range or even above 1 GHz, are alsocommonly used. It is a feature of the present invention to incorporate anovel tank filter on the RF telemetry pin antenna and at the same time,keep the RF frequency separation between the MRI pulse frequency and thetelemetry frequency as wide as possible.

It should be apparent that all of the aforementioned drawings showingconstruction of novel TANK filters 146 could also be accomplished withvarious other types of capacitor materials. That is, film capacitors,metallized film capacitors, tantalum, glass, porcelain, common aluminaelectrolytic and the like. For example, in a film capacitor applicationit would be obvious to replace the ceramic dielectric with a film. It isalso well known in the art to deposit metal or metallized surfaces ondielectric films. Accordingly, the aforementioned drawings showingprimarily monolithic ceramic or thick film deposition technology ismeant to be all encompassing to include all capacitor technologies. Aspecific example of this is understood by referring back to FIG. 81. Theblank cover sheets 348 and 352 could simply be some sort of a dielectricfilm, for example, Mylar or polystyrene. The capacitor electrode setcould be easily made of a flame sprayed metal deposition to formelectrode layer 340 and 342 (including very thin or with holes tocontrol R_(C)). In the same way, electrode layer 340 could be placed onanother layer of film. Then a blank piece of film could be put in placeof the blank interleaf 350. Additionally, metal could be deposited inanother area of the film capacitor forming the inductor layers 346. Afilm overlay could then be placed with additional cover sheet 352. Thiscould all be pressed and molded into a single package which is common inthe art of film capacitors.

Referring back to FIGS. 23 and 24, one can see the process of selectingthe appropriate values of L and C so that the TANK filter is resonant atthe correct frequency. This also shows how one can adjust the Q of suchcomponents to realize the curve shapes as described in FIG. 24. Asmentioned, it is highly desirable to have the TANK at or reasonablyclose to the resonant frequency, for example, of the MRI pulsedfrequency. It is not necessary that the TANK be exactly resonant at theMRI pulsed frequency if its resonant bandwidth is sufficiently broad. Inother words, even if the resonant frequency of the TANK was, forexample, 55 MHz in a 64 MHz MRI system, if the TANK resonant frequencycharacteristic has broad enough bandwidth, it would still providesufficient attenuation to effectively cool the distal TIP and providepatient safety.

Even after one goes through the decision making process in FIG. 23, itmay still be necessary to do some fine tuning of the TANK particularlyif it is constructed of very high Q components. There is a tradeoff herein that if very low loss capacitors and very low loss inductors are usedthen the bandwidth of the resulting TANK will be very narrow. In theart, this is known as a narrow 3 dB bandwidth. However, there isconsiderable manufacturing variability, for example, when manufacturingthe monolithic ceramic capacitors. This manufacturing variability isalso known as the tolerance. For example, for a ceramic capacitor of 50pf, it might have +/−20% tolerance based on the capacitance value. Thereis also variability in manufacturing the inductor elements themselves.Accordingly, for a very high Q TANK filter, it is expected that somefinal tuning may be necessary so that the resonant frequency of theresulting TANK is at or near the MRI RF pulsed frequency.

FIG. 119 illustrates a capacitor C and inductor L parallel combination,which is representative of any of the combinations discussed herein, ofthe present invention to form a novel L-C TANK 146. Referring to FIG.119, one can see a nozzle 600. This nozzle 600 is attached to a specialset of tubing 602 that comes from a microblaster (not shown) such asthat manufactured by Comco Corporation. Microblasters direct a jet ofhigh-pressure air containing particles 604 against any surface.Microblasters are well known in the art and are used for a variety ofcleaning and trimming operations. In this case, the microblaster 600could be filled with alumina ceramic which is a preferred cuttingmaterial. Referring once again to FIG. 119, one can see that anelectronic instrument 606 has been attached to both ends of the L-C TANKfilter 146. This is a scanning instrument such as a network or impedanceanalyzer that would be constantly measuring the resonant frequency ofthe TANK filter 146. The microblaster 600 can also be automated suchthat it is robotically dispensed and is turned on and off by theelectronic instrument 606. Such adjustments are easy to accomplishthrough Lab View and similar programming techniques. Referring onceagain to FIG. 119, one can see that a hole 608 has been literallyblasted away through the top cover layers of the ceramic capacitor C andinto its active electrode plates 610. This hole can be enlarged ordeepened as necessary to literally erode away a portion of the electrodeplate layers.

The microblasting goes on until the desired resonant frequency of theTANK 146 is achieved. It should be mentioned that the exact resonantfrequency of this tuning would not normally be the exact MRI pulsedresonant frequency. One might decide to tune slightly off to the side toaccount for the normal aging of the capacitor and/or inductor componentover time. That is, as the components age, they will stay within an areaof the TANK filter characteristic which provides a high degree ofattenuation.

FIG. 120 shows the electrode plate layer 610 taken from FIG. 119 insection 120-120. One can see that a portion of the active electrode 610has been eaten away. FIG. 121 is a view of the opposite electrode 612taken generally along the plane 121-121 from FIG. 119. This automaticprocess reduces the electrode plate overlap area which reducescapacitance value until the precise resonant frequency that is desiredof the parallel TANK 146 is achieved.

FIG. 122 illustrates a methodology of tuning a meander inductor 354 thatis co-bonded to the capacitor 614 forming the TANK filter 146 of thepresent invention. One can apply small dots of conductor material 616are used as required to short adjacent turns. This has the effect ofreducing the amount of inductance thereby allowing one to tune theparallel L-C TANK by adjusting the inductance downward. As previouslydescribed, for FIG. 119, this would typically be done while connected toan electronic instrument 606 which would give a constant readout of theresonant frequency. An alternative methodology is illustrated in FIG.123. In this case, the inductor pattern 354 has been deposited byvarious techniques, including screen printing, photolithography,electroplating and the like. However, in this case, deliberate shortingpaths have been manufactured between some of the inductor turns as shownat points 618-626. It is then possible to connect the composite L-C TANKfilter to the automated electronic instrument 606 used to measure theresonant frequency. Laser trimming or equivalent is then used toselectively remove the short circuits 618, 620 and so on until thedesired resonant frequency is achieved. A close-up view is shown in FIG.124 taken generally from 123 along section line 124-124. Referring onceagain to FIG. 124, one can see areas 618′ and 620′ where laser trimminghas occurred which opens up the previously shorted inductor turnsthereby increasing the inductance of the TANK. Referring back to FIG.119, microblasting is not the only way to make adjustments to acompleted capacitor. Laser trimming is also applicable to this procedureas well as high velocity water jet cutting or mechanical abrasion or thelike. After trimming is done in accordance with FIG. 119, it is typicalthat a dot of epoxy or a silicone or the like is used to fill theexposed hole 608. The inventors herein are familiar with these trimmingtechniques in the prior art for capacitors only. The inventors are notaware that such trimming techniques have ever been applied to a resonantcircuit such as the TANK filter 146 of the present invention.

FIG. 125 shows a novel unipolar feedthrough capacitor-inductor TANKfilter 382 embodying the present invention. A feedthrough capacitor TANK384 (with a co-bonded or embedded spiral inductor) similar to that shownin FIGS. 115-117 is embedded within a hermetic housing 386. The hermetichousing 386 consists of a biocompatible end plate which has a stub 388which allows for convenient laser weld attachment of the lead wire 104′(typically MP-35N alloy). These laser weld attachments are located at390 and optionally 392. The lead wire 104′ connects to the output of animplantable medical device 102 (See FIG. 17). The feedthrough capacitorTANK filter 384 is seated against the end plate 386 a using anon-conductive insulation layer 394. There is a similar insulation layer396 on the other side. These insulation layers 394 and 396 serve tomechanically seat the capacitor-inductor feedthrough capacitor TANK 384and hold it firmly in place as well as electrically isolate it. Thecylinder 398 is an alumina ceramic, glass or sapphire tube or the likewhich is insulative and hermetic. This is gold brazed or laser welded400 to the biocompatible end plate 386. The distal TIP 142 (tissuefixation clips not shown) is then inserted and seated into place and isthen also laser welded 402 to the insulative cylinder 398. Theinsulative cylinder 398 has been prepared to accept braze or weldmaterials by a previous sputtering or equivalent selective materialdeposition process. There is an electrical attachment 403 between thecapacitor outside diameter termination 404 and the electricallyconductive end plate 386. There is also an electrical attachment 405between the capacitor inside diameter metallization 406 and the distalTIP 142. This forms the novel TANK filter circuit 146 of the presentinvention by putting the capacitor (220) in parallel with its inductor L(380). The advantage of the structure illustrated in FIG. 125 is that itcomprises very low cost prior art capacitor and an efficient spiralinductor. Conventional non-biocompatible materials can be used tomanufacture the ceramic capacitor 220 and also to make the electricalattachments. Electrical attachments can include solders and thermalsetting conductive adhesives. This is because the ceramic capacitor 220and its corresponding electrical attachments are all hermetically sealedand isolated from body fluids. Accordingly, non-biocompatible materialssuch as silver and the like can also be readily used. Most commerciallyavailable monolithic ceramic capacitors are made with base metalelectrodes (BME) which contain nickel. As previously mentioned, nickelis undesirable both because of image artifact and its tendency to heatin the presence of MRI fields. Other common capacitor electrodes aremade from silver or palladium silver. However, silver and palladiumsilver, although relatively low in cost, are not biocompatible.Accordingly, the hermetic assembly of FIG. 125 allows the use of suchlower cost (low sintering temperature) electrodes. As previouslydescribed, for non-hermetic capacitors, platinum electrodes are used.The tradeoff is that platinum is more expensive and the capacitor mustalso be fired (sintered) at a much higher temperature.

FIG. 126 illustrates an alternative embodiment for a hermetically sealedTANK filter assembly 408. In this case, there is a distal TIP 142 whichis designed to intimately contact body tissue is shown on the left. Aninsulative cylinder 410 is preferably of either machined or pressedalumina ceramic, and includes sputtering 412 (such as atitanium-molybdenum layer) suitable for receiving a gold braze preform414. The cylinder 410 is attached to biocompatible electricallyconductive (preferably metallic) RINGS 144 and 144′ as shown. SinceRINGS 144 and 144′ will be exposed to body fluid, they must bebiocompatible and made of materials such as titanium, platinum or thelike. The distal TIP 142 is laser-welded at 416 to the electricallyconducting RING 144. The hermetic package shown by FIG. 126 is bestsuited for a rectilinear MLCC TANK 418 like those previously describedin connection with FIGS. 80, 81, 85 and 87. Electrical attachment ismade between the distal TIP 142 and the termination surface of theMLCC-T 418 by means of a solder or thermal setting conductive adhesive420. A gold sputter layer 422 or equivalent makes good electricalcontact between the conductive attachment material 420 and the distalTIP 142. The MLCC-T TANK end terminations are shown at 424 and 426. Athermal setting conductive adhesive, solder, braze or the like 428 isused to form an electrical connection between the TANK chip termination426 and a sputtered layer 422 on the back side of metallic plate 430.The typically titanium or platinum end plate 430 is similar to thatpreviously described in FIG. 125. It has attachments 432 for lead tolead wire 104′. The end plate 430 is designed to be laser-welded at 434to the biocompatible electrically conductive housing piece or RING 144′.Material 436 is a non-conductive thermosetting polymer or adhesive. Itspurpose is to provide mechanical support to the novel inductor capacitorchip 418. It can fill the entire space inside the hermetically sealedcontainer or only a portion as illustrated. A schematic diagram for thestructures of FIGS. 125 and 126 is shown in FIG. 127, wherein the novelcombination of the capacitor in parallel with the inductor which formsthe TANK circuit filter 146 of the present invention.

FIG. 128 illustrates an alternative hermetically sealed package thatcontains a novel inductor capacitor MLCC-T 438. In this case a hollowceramic or sapphire insulative tube 440 is utilized into which the novelMLCC-T 438 is inserted. A non-conductive thermosetting polymer adhesive442 is used to mechanically hold it in place. In this case there is ahelix active fixation electrode 444 which is designed to be screwed intobody tissue. This type of electrode is well known in the prior art andis used to firmly affix a distal TIP, for example, into myocardialtissue. There is a biocompatible metallic end plate 446 which has beenlaser welded at 448 to the insulative tube 440 and also laser welded at450 to the helix tip lead wire 444. At the opposite biocompatiblemetallic end RING 144 has been pre-attached by hermetic brazing or laserwelding at 452 to the insulative tube 440. Biocompatible metallic endplate 456 is typically made of titanium, platinum or the like. It willbe obvious to those skilled in the art for any of the inventions herein,that other biocompatible materials, such as tantalum, niobium and thelike could also be used. Referring once again to structure 456, one cansee that there is a sputter area 453 in order to provide a highlyconductive and oxide free surface. This sputter layer would typically begold, platinum or the like. Instead of sputter, this could also beapplied by gold brazing, plating or other techniques. A solder orthermosetting conductive adhesive preform 454 is used for the seating ofend plate 456. The end plate 456 is seated against this preform 454 andis then cured such that an electrical connection is made between the endplate 456 and the end metallization surface 458 of the MLCC-T 438. Thehelix TIP 444 has an electrical attachment 459 to the opposite endmetallization surface 461 of the MLCC-T 438. The end plate 456 isdesigned to be laser welded into the inside diameter (counter-bore) ofthe mating RING 144 forming a hermetic seal. The lead wire 104 comingfrom the implantable medical device is then attached by laser welding toa stub on the end plate 456 at point 460 and optionally at point 462.Additional attachment points can be added for additional mechanicalstrength.

FIG. 129 illustrates a distal electrode pad 464 applicable to a widevariety of neurostimulator applications. Neurostimulators includecochlear implants, deep brain stimulators, spinal cord stimulators,incontinence stimulators, general pain control stimulators, vagus nervestimulators, Parkinson's tremor control stimulators and the like.Typical prior art stimulators often come with a variety of pads such asthat shown in FIG. 129. Three neurostimulation electrodes 466, 466′ and466″ are shown, however, these can vary anywhere from one, ten or even20 or more neurostimulation electrodes. For example, in cochlearneurostimulators, there are commonly sixteen wires, which are insertedin a bundle of electrodes to make contact to the auditory nerves.Referring back to FIG. 129, one can see that there is a lead wire bundle468 which contains three wires that are connected to an external orimplanted active medical device.

FIG. 130 is a cross-sectional view taken generally along line 130-130 ofFIG. 129, and illustrating one form of the novel inductor capacitorMLCC-T 470 of the present invention. One can see that there is adiscoidal feedthrough capacitor 220 with an air core inductor 472running through its center. These concepts were previously described inconnection with FIGS. 45 and 47. In this case, the distal TIP electrodepad 466 has a laser weld or equivalent biocompatible electricalattachment 474 to the surrounding metallization of the capacitor 220.There is also another conductive plate 476 shown connected to theinductor 472 on the opposite side. Lead wire 478 is in turn mechanicallyand electrically connected to this plate 476. Lead wire 478 is thenrouted through the flexible neurostimulator pad 464 as shown in FIG.129. Lead wire 478 becomes part of the wire bundle contained in 468which would be routed to the AIMD.

FIGS. 131 and 132 describe alternative ways of accomplishing the samething using a feedthrough capacitor structure as previously described inFIGS. 115 and 118 in the electrode pad 465. In this case, the inductor380 has been printed onto the top of the capacitor 220 or attached tothe capacitor by means of a supplemental substrate. Lead wire 478 isconnected to the capacitor's internal diameter metallization 406 asshown using an intermediate contact plate 480. The electrode 466 iselectrically and mechanically attached to the capacitor outside diametermetallization 404, but electrically insulated from the internalmetallization 406, such as with an insulative pad or liner 481. This isshown inverted for simplicity as compared to FIG. 129.

FIG. 133 illustrates another alternative using thick film techniques tobuild up in layers the novel parallel inductor TANK filter forneurostimulator applications as previously shown in FIG. 129. Again,this electrode assembly 483 is shown inverted for simplicity. The distalTIP electrode 466 forms a substrate such as used for thick filmdeposition of various capacitor and inductor layers. The structure 483of FIG. 133 is better understood by looking at the exploded view in FIG.134. Starting at the bottom we have the distal TIP electrode pad 466 forneurostimulator applications. An insulative layer 482 is first imprintedon this conductive electrode 466 and then one or more inductor layers484 are imprinted thereon. Then another insulative layer 486 is laid ontop of the inductor layer 484. Onto this a capacitor inner diameterelectrode 488 is printed. Then another insulative layer 490 is printed.Then an outside diameter capacitor electrode 492 is imprinted. Manyalternating layers of electrodes 488 and 492 can be stacked up asdesired to achieve the required capacitance value. Then an overallinsulative layer 494 is laid down. As is well known in conventionalthick film or tape manufacturing processes, there is usually a dryingstep between each one of these operations. The entire structure is thensintered at high temperature to form a rugged monolithic structure. Anelectrical contact 496 is then inserted using a suitable electricalconnection material to make contact with both the inside diameter of theinductor 486 and the inside diameter of the inner diameter capacitorelectrode plate stack 488. In turn, neurostimulator lead wire 478 iselectrically connected to this contact pad insert 496. The outsidediameter of the inductor makes contact with neurostimulator pad 466. Thecapacitor's ground electrode plates 492 also make electrical contactwith the distal pad electrode 482. This has the effect of putting thecapacitance in parallel with the inductance in accordance with the TANKfilter of the present invention.

Table 135 illustrates various fabrication methods for manufacturing thethick film TANK circuits described in FIGS. 133 and 134.

FIG. 136 is an alternative rectilinear embodiment to build a thick filmTANK filter of the present invention. This also uses similar fabricationtechniques that were described in FIGS. 134 and 135. This starts with asubstrate 498, onto which the various layers 504-514 are eitherimprinted or laid down. There are two convenient wire bond pad areas 500and 502 suitable for connection of neurostimulator lead wires.

FIG. 137 is a schematic diagram of the neurostimulator electrodespreviously described in FIG. 136, and is equally illustrative of FIGS.130, 132, and 133.

FIG. 138 is an exploded view of the neurostimulator electrode 495 ofFIG. 136, showing how the various layers of the novel distal TIP TANKcircuit are laid down. As shown, one starts with the substrate layer498. In this case, the substrate layer is insulative and could be of anysuitable circuit board material such as alumina and the like. Acapacitor electrode layer 504 is printed down onto the substrate 498.This is overlaid by an insulative layer 506. Then the second capacitorelectrode 508 is laid down and again, and another insulative layer 510is laid down over the top. A novel inductor shape 512 is then imprintedon the insulative layer forming a parallel TANK filter circuit 146.Shown is a meander pattern, although any of the previously describedpatterns can be used. On top of this is a final insulative layer 514 forboth mechanical and cosmetic reasons. As previously described, as manycapacitor electrode layers 504 and 508 can be laid down as required toachieve the desired capacitance value. In addition, multiple inductorlayers 512 could also be laid down to achieve a desired inductance and adesired inductor resistive loss (R_(L)).

FIG. 139 illustrates the novel inductor TANK filter previously describedin FIG. 136. In this case, the thick film inductor capacitor TANK hasbeen hermetically sealed by overlaying with a suitable glass seal 516.This glass 516 can be deposited as a frit or molten and then sintered athigh temperature. The glass is designed to adhere to the substrate 498and the wire bond pads 500 and 502 such that it forms a hermetic sealover the entire TANK filter of the present invention. Material 516 canbe any number of borosilicate or compression glasses or even polymersealants such as silicone and the like.

FIG. 140 is a representation of how one could also glass hermeticallyseal 516 any of the novel TANK filters of the present invention. Forexample, reference is made to FIGS. 35, 37, 42, 44 and 58 for just a fewexamples of novel inductor capacitor TANK filters 146 that can beenclosed within a hermetic sealed package as illustrated in FIG. 140. Itwill be obvious to those skilled in the art that the hermetic seal couldbe of ceramic, sapphire, glass and can be sealed in a variety of ways toprevent the intrusion of body fluids into the sensitive capacitor orinductor element embedded therein. The hermetic seal structure shown inFIG. 140 is easiest done by glass. There are a number of prior art glasssealing processes that are used for capacitors and diodes and the like.In the art, many of these are known as DAP sealers.

FIG. 141 illustrates the use of a prior art feedthrough capacitor 220with co-bonded inductor spiral substrate 518 of the present invention.The inductor spiral has been imprinted or deposited on a substrate 520as shown. The composite structure has metallization surfaces 226 and 228for convenient electrical attachment into a lead wire system or incombination with a distal TIP as described herein. When co-bondedtogether, the combination shown in FIG. 141 forms the novel parallelinductor capacitor TANK filter 146 of the present invention. Referringto FIGS. 89-92, one can see that the inductor spiral substrate 520 shownin FIG. 141 could have a number of parallel inductor layers 118.

FIG. 142 is an isometric drawing of a composite unipolar MLCC-Tfeedthrough 522 of the present invention. This is best understood byreferring to the stack up of layers as shown in FIG. 143.

From top to bottom there are several thin ceramic cover sheets 524 asshown. Then there are one or more inductor layers 518 as shown separatedby a ceramic insulator 526. Then there are a plurality of inner diameterelectrodes 528 and outer diameter electrodes 530. These alternatinglayers can be stacked up to achieve the desired capacitance required.This is finished off by insulative ceramic cover sheets 532 as shown.These are pressed, laminated and then fired at high temperature to formthe rugged monolithic structure shown in FIG. 142. Metallization bands534 and 536 are then added for convenient electrical attachment. Thecross section of the composite TANK filter 522 of FIG. 142 is shown inFIG. 144.

FIG. 145 is a cross-sectional view of a generic prior art activefixation distal TIP 628 typically used in conjunction with cardiacpacemakers. These active fixation TIPs 628 are well known in the priorart including the following patents all of which are incorporated hereinby reference: U.S. Pat. Nos. 7,092,766; 6,952,613; 6,931,286; 6,876,885;6,687,550; 6,493,591; 6,141,594; 6,055,457; 5,759,202; 5,741,321;5,716,390; 5,545,201; 5,514,173; 5,300,108; 4,858,623; 4,799,499; and4,858,623. In FIG. 145, one can see that there is a metallic housing 630which contains a sharp tipped distal helix coil 632. This helix coil 632is designed to be extended and screwed into body tissue. It is shown inits retracted position. This is to enable the physician to insert thedistal TIP assembly 628 through the venous system, through the atrium,and into the ventricle so it does not snag or tear on any tissue. Onceit is in the appropriate position, the physician then turns lead wirespline assembly 634 in a clockwise rotation. This is done outside thepectoral pocket with the lead wire protruding from the body. A tool isgenerally applied so that the physician can twist or screw the helix 632into place. Protrusion 636 acts as a gear so that as helix 632 isturned, it is screwed forward. This makes for a very reliable fixationinto myocardial tissue. Helix 632 is generally laser welded to aprotrusion 638 on the spline 634 as shown. Of course, all of thematerials shown in FIG. 145 are biocompatible. Typically, the helix 632is made of platinum iridium alloy and would be coated with variousmaterials to improve electrical performance. Housing 630 would generallybe composed of titanium or other equivalent biocompatible alloy. Thespline 634 is generally a platinum iridium alloy. Attached to spline634, usually by laser welding, is the lead wire 640 coming from theAIMD. An optional feature 642 is placed on spline 634 to create apositive stop as the physician is turning the lead wire assembly andscrewing the helix 632 into body tissue. A secondary stop occurs whenthe gear feature 636 engages the end of the turns down near the laserweld 638.

FIG. 146 is a sectional view taken generally from section 146-146 inFIG. 145, the stop 642 has been replaced with a hermetically sealed tankfilter 644 of the present invention. In general, the tank filter can beseen placed in series with the lead wire of the AIMD in FIG. 17. Thetank filter of FIG. 42 could be used in this position as long as allbiocompatible components were used. Referring to FIG. 65, this couldalso be placed in series with the lead wire system if the distal TIPfeature 142 was replaced with an equivalent insulative feature so thatthe lead wire could be placed in series. In other words, the distal TIPwould be replaced with a cap similar to 308. One could also incorporatethe novel tank of FIG. 94 which incorporates the coiled lead wiresencircling a novel MLCC capacitor composed of entirely biocompatiblematerials 332. One could also install the novel feedthrough capacitorcoaxial tank of FIGS. 115 and 117 as shown in FIG. 146 as feature 644.In a preferred embodiment, one could incorporate the glass hermeticallysealed encapsulated tank previously described in FIG. 140.

FIG. 147 is an adaptation of FIG. 145, including an MLCC-T 646 of thepresent invention. FIG. 147 shows the prior art active fixation distalTIP 628 previously described in FIG. 145. The tank filter MLCC-T 646 isshown in close proximity to the helix TIP 632. By having the distal TIPtank filter 646 in immediate proximity to the distal TIP 632, one canprevent the flow of MRI-induced RF pulsed currents into myocardialtissue. Referring once again to FIG. 147, one can see the lead wire 640is routed from the output of the implantable medical device. Typically,this lead wire 640 would be constructed of biocompatible alloy MP-35Nand laser welded at points 648 and 650 as shown. Optional stop 642 isshown and can be laser welded in place 652. This would typically be doneafter assembly. A novel feature of the present invention is thatassembly of the entire MLCC tank filter 646 can be done with the helix628 outside of its housing 630. This allows for easier electrical andmechanical connections (assembly), and enables high reliabilityscreening of the tank 646, such as thermal shock, burn in, and the like.This is very important so that the MLCC tank 646 will be highly reliablein the patient application. Once all of this testing has been done, theentire assembly consisting of helix 632, MLCC-T 646, flange 654 andspline 634 can be inserted by screwing it into the assembly 628 from theright hand side of the cylinder 630. Then, novel end cap 656 is placedover the spline shaft 634 and laser welded 658 in place. It is notnecessary that laser weld 658 be 360 degrees (only spot attachments arerequired). Subsequently, stop 642 can be laser welded in place 652 ontothe shaft 634 as shown. Then the lead wire 640 consisting of MP-35Nalloy can be laser welded at points 648 and 650 as shown. This completesthe assembly.

FIG. 148 is a fragmented sectional view taken generally from section148-148 from FIG. 147, illustrating the MLCC tank 646 consistinggenerally of the inductor assembly 660 and the feedthrough capacitor662. The feedthrough capacitor 662 has been previously described in thedrawing description of FIG. 39. Referring to FIG. 148, one can see thata protrusion 664 has been added to the spline shaft 634 so that thefeedthrough capacitor 662 inside diameter 666 can be electricallyconnected 668 to it. This electrical connection material is shown as668, and would generally be of the group of thermosetting conductivebiocompatible polymers. There are a number of alternative materials thatcould be used including various biocompatible solders, brazes, welds,conductive glasses and the like. The electrical connection 668 isbetween the platinum spline material 664 and the inside diametermetallization 666 of the feedthrough capacitor. There is an insulativematerial 670 between the feedthrough capacitor 662 and the spline flange664. The reason for this is to be sure that a short circuit does notoccur between the capacitor outside diameter metallization 672 and thespline pedestal area 654. There is also an electrical connection 674between the capacitor outside diameter metallization 672 and theinductor outside metallization 676. There is an equivalent electricalattachment 678 shown between the conductive spline protrusion 664 andthe opposite of the end of the inductor metallization 676.

There is an optional insulating tube or sleeve 680 shown. Thisinsulating sleeve 680 is to insure that neither the inductor 660, thecapacitor 662, nor the distal helix 632 short (electrically contacts)against the metallic housing 630. In this preferred embodiment, afterall of the high reliability testing is completed, the entire assemblyconsisting of the spline pedestal 654, the feedthrough capacitor 662,the co-attached inductor 660 and the first two turns of the helix 632would all be parylene coated. Parylene is a highly biocompatibleinsulative material that is generally deposited by vacuum depositionchamber techniques. A coating of parylene over all surfaces providesboth excellent insulation and an additional degree of immunity to bodyfluids. In a case where parylene coating was placed over all surfacesthen optional insulating layer 680 could be eliminated.

Referring once again to FIG. 148, one can also see that the end cap 656has been laser welded 658 in place. This is done after the entire noveltank assembly 646 including distal TIP has been high reliability testedand then threaded into place.

The construction of the novel inductor 660 will be better understood byreferring to FIG. 149, which is generally taken from section 149-149from FIG. 148. This is the exploded view of the novel inductor structure660 that was previously shown attached to the feedthrough capacitor 662in FIG. 148, and illustrated in FIG. 149A. One can see that the inductor660 has been exploded into four slices as shown. Starting from the top,slice 682 generally consists of an alumina ceramic material with a viathrough hole 684. It also has a metallized wire bond pad surface 686 asshown. This is designed to be mated and co-fired to slice 688. As onecan see, a novel inductor spiral of the present invention 690 has beenimprinted onto the alumina substrate of slice 688. One should also notethat the via hole 684 is aligned over the end of the inductor spiral 692after they are mated. This allows the via hole 684 to be filled withconductive material such that an electrical connection is made betweenwire bond pad 686 and the central end of the inductor spiral 692. If onenow follows that inductor spiral, one will see via through hole 694 asshown. Via hole 694 is carefully positioned so that it will align overthe peripheral or outer end 696 of the inductor 698 shown in slice 700.This allows via hole 694 to be filled with conductive material, therebymaking an electrical connection between 694 and 696. If one then followsthe inductive spiral 698 on slice 700 to its end at via through hole702, one can see that via hole 702 has been lined up to align with theend 704 of the inductor 706 from slice 708. Again, filling the via hole702 with a suitable conductive material forms an electrical connectionbetween 702 and 704 as shown. Referring once again to slice 708, if onefollows the inductor pattern 706 around to its outside diameter, one cansee that there is a full circumferential electrode exposure 710. Afterthis completed assembly consisting of slices 682, 688, 700 and 708 hasbeen assembled and co-fired, one can then apply the externalmetallization 712 around its complete outside diameter. This exteriormetallization 712 makes electrical connection in slice 708 to theoutside of the inductor 710.

It will be obvious to those skilled in the art that any number ofinductor layers n can be used. It is also not necessary that the numberof turns or even the inductor shape be the same in each one of theslices. The number of turns, the widths, pitch, and the total length ofthe inductors can all be varied as desired to achieve the totalinductance that is required for the particular design. In addition,referring back to FIG. 149, all of the materials and all of the viaswould preferably be of suitable biocompatible materials. In practicethis would mean that, in a preferred embodiment, the substrates (slices682, 688, 700 and 708) are of ultra high purity alumina ceramic and theinductor traces 690, 698 and 706 are all of pure platinum or equivalent.In addition, the via hole fills would likely be of pure gold orequivalent biocompatible material. An alternative way to fill the viaholes would be to use a thermosetting conductive biocompatible polymeras previously described in FIG. 148.

Referring back to both FIGS. 148 and 149, it will be appreciated thatthe use of mechanically robust structures are required. That is due tothe great deal of torque and sheer stresses that will be placed on theelectrical components when the physician turns the spline shaft 634 andscrews the helix 632 into myocardial tissue. Also, during the life ofthe device, as the helix 632 is attached into myocardial tissue, thereare flexures, shocks and vibrations occurring during each beat of theheart. Accordingly, there is a need for both the inductor structure 660and the feedthrough capacitor 662 to be quite mechanically robust. It isa general principle in ceramic engineering that the higher the k of thematerial, the lower the mechanical strength of that material. Theconverse is also true. The use of very low dielectric constant (low k)ceramic materials result in higher mechanical strength. The dielectricconstant of alumina is approximately 6 to 7. The dielectric constant ofvery high k ceramic capacitor dielectrics can exceed 3000. However,these 3000 k dielectrics are mechanically very weak. It is a novelfeature of the present invention that the feedthrough capacitor 662 andthe inductor 660 as shown in FIG. 148 be constructed of relatively low kceramic materials. Electronic Industries Association (EIA) has a seriesof standards that specify the electrical characteristics of variousceramic dielectrics. NPO, which is specified by the EIA standard and iswell known in the prior art and has a k between 60 and 90, would be anideal choice in this case. For the inductor 660 as illustrated in FIGS.148, 149 and 149A, the use of alumina ceramic would be ideal since it isrelatively low in k and is also very strong. Another suitable materialfor either the capacitor 662 or the inductor 660 is the use of manganesetitanate (porcelain). Manganese titanate has a k between 10 and 12 andgenerally has NPO capacitor characteristics. This material has a veryhigh Tensile strength, a very high yield point and it also has a veryhigh modulus of toughness. Accordingly, manganese titanate would be anideal candidate for the present application. In addition, there are anumber of commercially available NPO dielectrics which are compatiblewith a ternary electrode system. A ternary electrode system consists ofgold, platinum and palladium, all of which are biocompatible.

Referring once again to FIG. 149, one can see that, in the preferredembodiment, the substrate layers 682, 688, 700 and 708 are all of highpurity alumina. The reason is that alumina is very low in k (less than10) and is also very mechanically robust. In fact, alumina is commonlyused in implantable medical devices for the hermetic seal where leadwires pass in and out of an implanted medical device.

In another preferred embodiment, it is desirable to completely eliminatefeedthrough capacitor 662 as previously described in FIG. 148. This canbe done by taking advantage of the fact that multiple inductor spirals,as shown in FIG. 149, have been added in series. This is betterunderstood by referring to the schematic diagram in FIG. 150. One cansee that the inductor spirals of slices 688, 700 and 708 are added inseries where in L_(TOTAL)=690+698+706. Referring back to FIG. 150, therewill be a distributive capacitance C_(P1) between the adjacent turns ofeach one of these spiral inductors. This will be substantially higherthan would occur in an air wound solenoid inductor. This is because airhas a low dielectric constant relative to alumina or other dielectricmaterials. Also, compared to alumina, body fluids also have a relativelylow dielectric constant. Another reason one would not want to put an airwound inductor into body fluids is the conductivity of body fluidsthemselves, which would tend to short adjacent inductor turns.

In FIG. 150, one can see that there is a parasitic capacitance C_(P1)that actually occurs between every turn of the spiral inductors 690, 698and 706 previously illustrated in FIG. 149. These will add up to a totalparallel inductance as shown in FIG. 150 as C_(P). One can see that in apreferred embodiment, one could adjust this total parallel capacitanceC_(P) such that it would be resonant with L_(TOTAL) (690+698+706) at theRF pulsed frequency. In this way, one could completely eliminate thefeedthrough capacitor 662 as a separate element. This composite MLCC-Tintegrated assembly 714 is shown in FIG. 151.

FIG. 151 is similar to the novel MLCC tank assembly 646 previouslyillustrated in FIGS. 147 and 148 wherein the tank and filter of thepresent invention has been incorporated inside the coaxial cylinder 630of an active fixation distal TIP 628, for example, that of a cardiacpacemaker. In FIG. 151, the same three inductor spiral slice substrates688, 700 and 708 are present as previously described in FIG. 149.However, wire bond pad area 716 has been electrically separated fromwire bond pad area 718. Accordingly, the total series inductanceconsisting of 690+698+706 can be directly measured by connecting aninductance bridge between 716 and 718. Referring to substrate 708, onecan see parasitic capacitance C_(P). As previously stated, a parasiticcapacitance occurs between each turn of these spiral windings. Theseparasitic capacitances can be controlled by controlling the width,spacing and number of the various spiral turns. Each one of the inductorsubstrate layers 688, 700, 708 (or n substrate layers) will all have aself resonant frequency that depends upon the total amount ofcapacitance and the total distributive capacitance (primary resonance).There will also be secondary resonances that occur (adjacent turnresonances).

FIG. 152 is an electrical schematic diagram of the structure 714 shownin FIG. 151A. Referring to substrate layer 688, one can see that thereis a parasitic capacitance CP₁ that ends up in parallel with the totalinductance 690. A similar thing happens for substrate layers 700 and708. By carefully controlling the parasitic capacitance and the parallelinductance, one can create multiple resonant frequencies. For example,we could have substrate layer 688 resonate at 64 MHz, substrate 700resonate at 128 MHz and substrate 708 resonate at close to 216 MHz. Itshould also be pointed out that with multiple resonances like this, itis not even important that each substrate layer resonate exactly at theMRI RF pulsed resonant frequency. All that is really important is tokeep the impedance high throughout this range. This is best examined bylooking at FIG. 153, which is a graph of the impedance versus frequencyof the tank circuit of FIG. 150. As one can see, there are multipleresonances occurring between 64 MHz, 128 MHz, 216 MHz and even higher.This is highly desirable in that it keeps the impedance, and therefore,the attenuation to MRI-induced RF currents very high throughout thedesired range.

FIG. 154 is an isometric drawing of a unique integrated tank filter 720of the present invention. It consists of parallel inductors and parallelcapacitors as further illustrated in the schematic drawing of FIG. 155.This is best understood by referring to the exploded view shown in FIG.156. In FIG. 156, we can see that there are various substrate layers 722through 730. Substrate layer 722 is a cover sheet with a via hole 732and a metallization surface 734. The via hole 732 is designed to alignwith via hole 736 in substrate 724. Inductor 738 is formed in substrate724 and is terminated all around the outside circumference also shown as740. The exterior or outside diameter of the assembly 720 also hasmetallization shown as 742 in FIG. 154. A capacitance is formed betweenthe overlap area of the inductor trace 738 and the capacitor groundelectrode 744 shown in substrate layer 726. One can see that there isalso a via hole 746 that passes through in non-conductive relation withthe electrode 744 down to electrode layer 728. Filling of the via hole732, 736 and 746 makes an electrical connection all the way from the topmetallization layer 734 down to the electrode pad 748 at the center ofinductor spiral 750 shown in substrate 728. A second capacitor 752 isformed between the overlap of inductor trace 750 and the capacitorelectrode metallization 752 shown in substrate layer 730. As describedfor substrate layer 726, the capacitor electrode metallization 752 comesto the outside diameter where it makes contact with the outside diametermetallization 742. All of this has the effect of putting parasiticcapacitance between the electrode traces in parallel with one another asshown in the schematic in FIG. 155. Having the two capacitors 744 and752 in parallel is highly efficient because capacitors in parallelsimply add together. However, having the two inductors 738 and 750 inparallel is not particularly efficient because the amount of inductanceis thereby reduced in accordance with the parallel inductance formula.

Referring once again to FIG. 149, one can see a novel technique ofplacing inductors in series. Inductors in series simply add togetherthereby directly increasing the overall inductance. If one refers tosubstrate layers 688, 700 and 708 taken from FIG. 149, one can easilyenvision how they could replace substrate layer 730 previously shown inFIG. 156. In this way, one could greatly increase the inductance of theFIG. 156 structure 720 by using these series techniques that werepreviously described in FIG. 149. One skilled in the art will realizethat the inductor substrate layers 688, 700 and 708 taken from FIG. 149could be used to replace substrate layer 730 or substrate layer 726 ofboth as desired in order to achieve the total amount of inductanceneeded.

FIG. 157 illustrates a methodology of integrating both techniques ofinserting capacitor ground electrode plates 726 and 730 while at thesame time having series inductor elements 688, 700 and 708. Thecomposite structure is shown at the bottom of FIG. 157 as 720′, which isvirtually identical to the isometric drawing of the novel tank 720 shownin FIG. 154.

FIG. 158 illustrates applying the novel tank filter 714 of FIG. 151 to aprior art active fixation distal TIP 628 previously described in FIG.147. Referring once again to FIG. 158, one can see the attachment fromthe metallization 718 of novel tank MLCC-T 714 from FIG. 151 shownattached to the spline and spline pedestal 634 and 654. This istypically accomplished by a gold braze preform 756. In this case, thepedestal 654 has been counterbored to receive the end of the novelMLCC-T tank filter 714. This allows the gold braze material 756 to angleup along the sides of the MLCC-T 714, thereby adding sheer strength tothe overall assembly. It will be obvious to those skilled in the artthat this same counterbore could also be applied to the helix pedestalpost assembly 758. This would allow gold braze material 760 to also comearound the sides of the novel MLCC-T tank filter 714 to provide sheerstrength in that area also. A similar gold braze preform 760 is used toattach a distal TIP helix pedestal 758 to the metallization 716 of thenovel tank MLCC-T 714. Of particular advantage is that the novel MLCC-Tsubstrate illustrated in FIG. 151 can be constructed entirely of low k,very high strength ceramics. In this case, pure alumina or porcelainwould be preferred embodiments. These have the advantage of beingmechanically very rugged and also very rugged to thermal shock such thatit would take pure gold brazing. By use of all biocompatible materials,the assembly is greatly simplified in that it need not be hermetic. Itwould also be possible to replace the gold brazes 756 and 760 withequivalent laser welds. Referring once again to FIG. 158, one can seethat the end cap 656 has been modified in a novel way such to make itflush with the outside diameter of the active fixation TIP assembly 630.This allows one to increase the inside diameter allowing room for thenovel counterbore as previously described in pedestal 654. The metallicend cap 656 has been stepped so that it is seated for convenientfixturing and also a countersink 762 has been applied for convenientgold brazing or laser weld material 658.

FIG. 159 is an adaptation of the generic prior art active fixationdistal TIP 628′ previously illustrated in FIG. 145. References also madeto FIGS. 147, 148 and 158. All of these previous drawings have twothings in common: 1) they allow body fluid to freely penetrate to allsurfaces interior to the active fixation distal TIP 628; and 2) torqueexperienced by the helix 632 is transmitted to any electronic component,such as the tank of the present invention and its associated electricaland mechanical connections. Referring now back to FIG. 159, the splineshaft 634 has been modified such that it has a relatively long, hollowcylindrical portion 654′ which allows for the insertion of the tankfilter 146 of the present invention inside of it. As will be seen, thiswill offer a number of important mechanical and biocompatibilityadvantages. The tank 146 that is shown in FIG. 159 is the tubularintegrated MLCC tank 320 previously described in FIGS. 68-76. Forsimplicity, the internal electrode plates 324, 326 and 328 that form thecapacitor and inductor elements are not shown in FIG. 159 since any ofthe aforementioned embodiments can be incorporated. It will also beobvious to those skilled in the art that the novel tank filters 146 thatare described in FIGS. 32, 35, 37, 42, 44, 65, 80, 83, 85, 87, 115, 126,128 and 141 can all be easily incorporated into the novel housing 654′as illustrated in FIG. 159. Referring once again to FIG. 159, one cansee that the tank filter 146 of the present invention is first insertedinto an insulative liquid material 762. This is then cured, which holdsthe tank filter 146 in place. It also performs another importantfunction in that the metallization surfaces 764 and 766 of the tankfilter 146 are prevented from shorting out against the bottom of 654′.The material 762 could also be a non-conductive washer, a thermosettingnon-conductive polymer or the like. There is an electrical connection768 that is generally made of a thermosetting conductive polymer thatmakes an electrical connection between the typically platinum spline 634and cup 654′ assembly and the outside diameter termination 766 of thenovel tank 146 of the present invention. There is a correspondingelectrical connection using similar materials 770 that connects betweenthe inside diameter metallization 764 of the novel tank 146 of thepresent invention and pedestal post lead wire 772. Alternate electricalconnection materials 768 and 770 could also be of the group of solders,brazes, welds and the like that are typical in the prior art. One cansee by referring to FIG. 159, that there is a large advantage to thesurrounding cylinder 654′. The rather sensitive electronic devicesconsisting of the inductor and the capacitor element are nowmechanically protected by the surrounding metal material. Duringphysician implant, where the entire assembly is twisted and the helixTIP 632 is screwed into body tissue, this means that the interiorcapacitor and inductor elements are completely protected and not exposedto those forces. In the ongoing application in the patient environment,there is an associated stress with every beat of the heart which tendsto fatigue and cause shock and vibration loads to this entire assembly.Again, by having the sensitive capacitor and inductor elements 146completely enclosed, they are protected from such forces. There isanother advantage to the assembly shown in FIG. 159 in that it iscompletely hermetically sealed. The hermetic terminal assembly is firstformed using prior art gold brazing or glass sealing techniques. Thishermetic seal subassembly will consist of ferrule 774, alumina ceramicinsulator 776 (or glass or equivalent) and the unique pedestal postone-piece assembly 758′ consisting of features 772, 778 and 780. Anoptional spacer washer, typically consisting of alumina, 782 is used toprevent the pedestal feature 778 from shorting out to the ferrule 774.It is very important that these be kept in electrical insulativerelationship. As in all prior devices, the helix 632, that is designedto be screwed into body tissue, is laser weld attached to the pedestal778 at point 638.

Referring now back to the hermetic terminal seal assembly, one can seethat the hermetic seals are formed by gold brazes 784 and 786 whichmakes attachment between the alumina ceramic 776 and the metal joints772 and 774. Not shown is a typical first operation wherein the aluminaceramic 776 is first prepared by sputtering typically with a layer oftitanium and then a layer of molybdenum. The first layer is the adhesionlayer and the second layer provides for good wetting of the gold braze.This is all well known in prior art. The entire hermetic sealsubassembly is then laser welded in a continuous 360 degree laser weldas shown in 788. This completely hermetically seals the novel tankfilter of the present invention.

Referring once again to FIG. 159, one can also see that there is an endcap 656′ which is flush with the outside diameter of the housing 630 ofthe active fixation distal TIP assembly. As described before, this willbe added after the entire assembly is screwed into place as a last step.It will be obvious that FIG. 159 can also have an insulating sleeve (notshown) around the outside diameter of the complete assembly consistingof 654′. In addition, the entire assembly could be parylene coated aspreviously described (also not shown). Referring back to the end cap656′, one can see that it is laser welded in place 658. It is notnecessary that laser weld 658 be 360 degrees. In fact, for ease ofassembly it would only be spotted in a few places.

An additional advantage of having the capacitor inductor element of thetank filter 146 inside the housing 630 of the active fixation TIP 628 isthat this provides a substantial degree of protection to these delicateelectronic components. Doctors and other medical personnel are oftennotorious in the way they handle lead systems. Things can get dropped,moved or placed against them. Accordingly, having these devices insidethe metal housing is highly desirable.

FIG. 160 illustrates a prior art neurostimulation electrode probe 540 ora common ablation probe or a catheter that is commonly known in theprior art. As one can see, there are a multiplicity of stimulationelectrodes 542-542′″. In this particular application the end tip 544 isinsulative.

FIG. 161 is the prior art probe 540, neurostimulation TIP or catheter ofFIG. 160 re-drawn to include novel MLCC-T TANK filters 146 and 146′ ofthe present invention (146″ and 146″ are not shown for simplicity). Inthis particular case these TANK filters are similar to those illustratedin FIG. 141 or 142. One can see that these are placed in conjunctionwith the stimulation electrodes 542, 542′ and so on. As many as desiredcan be stacked as shown. This has the effect of placing the novel TANKfilter of the present invention in series with each one of thestimulation rings and thereby limiting/preventing the flow of MRIinduced RF currents.

A feature of the present invention that conventional low pass EMIfiltering is still provided at the input to the AIMD which is verybroadband in nature. However, it may still be highly desirable tocontrol the specific MRI pulse frequencies through use of novel TANKfilters placed strategically within the lead wire system. This can be atthe distal TIP, along the lead wire system or at the point of lead wireingress into the AMID housing. This is best understood by referring toFIG. 162 where the novel TANK filters 146-146′″ of the present inventionare shown strategically placed at the point lead wire ingress (comparewith FIG. 2).

Referring now to FIG. 163 one can see a prior art broadband low passfeedthrough capacitor 120 as previously illustrated in FIG. 3. In thiscase, lead wire 104 a has been broken into discontinuous nail headsegments 550 and 552. A novel MLCC-T 344″ of the present invention isshown as taken from FIG. 87. This novel TANK filter circuit is locatedwithin location plate 554. This location plate could be an aluminaceramic, plastic or any other insulative material suitable for locatingthe novel inductor TANK chips MLCC-T 344″. This thin plate 554 couldalso be an inductor slab as described in U.S. Pat. No. 6,999,818. Theelectrical attachment between the lead wire segments 550 and 552 to thenovel MLCC-T 344″ are made by electrical connection material 556 and558. These electrical connection materials could be a thermal settingconductive adhesive, solder, braze or the like. The presence of theMLCC-T 344″ in series with a lead wire offers a much higher degree ofprotection at selected MRI pulse frequencies to the sensitive internalelectronics of the AIMD. In addition, this presents a very highimpedance in the lead wire system of the AIMD. Since the equivalentcircuit of an AIMD lead wire consists of many series inductance,resistive, and parallel capacitance elements that are multiple loops andresonances within the overall lead wire system. Accordingly, placing theMLCC-TANK filter of the present invention only at the distal TIP may notprevent problems with overheating of a lead wire system near the AIMD.It has been shown in the literature that overheating of the lead wireimmediately adjacent to an AIMD can, using a pacemaker as an example,lead to venous ablation (burning of the subclavian vein) or esophagealablation or burning. Accordingly, having a high impedance in the leadwire system near the AIMD offers particular advantages in that lead wirecurrents and associated heating would be reduced or eliminated.

FIG. 164 shows an alternative method of installing MLCC-T TANK filters146 of the present invention in series with prior art broadbandfeedthrough capacitor filters 120. FIG. 165 illustrates how coaxialcapacitors that have been previously described in FIGS. 65 and 68-73could all be used in combination with a prior art feedthrough capacitor120 to achieve the desired properties previously described in connectionwith FIGS. 163 and 164.

FIG. 166 is a schematic diagram of the novel MLCC-T TANK filterspreviously described in FIGS. 163-165. One can see the MLCC-TANK filtercircuit 146 of the present invention placed in series with the prior artfeedthrough capacitor 120. This can be unipolar (1), bipolar, tripolar,quadpolar or many leads as desirable. In certain cardiac therapyapplications there could be as many as twelve or more of these inparallel. The present invention incorporating a novel MLCC-T TANK filteris also very useful for various types of robotically or remotelycontrolled surgical operations. For example, in remote controlledsurgery, electrocardery devices such as BOVI knives are commonly used.Anything that is placed inside the body that requires real time MRIguiding must be protected from the effects of overheating or damage toits own electronics. Accordingly, the present invention is adaptable toany of these robotically controlled surgical operations.

FIG. 167 illustrates a prior art skin electrode pad 466. This could be asurface electrode pad used for ECG/EKG cardiac monitoring. Such pads canbe as many as 12 lead systems 478 or more. These skin electrodes aretypically stick on the chest and other places around the body (and evenon the feet). The skin electrode pads 466 shown in FIG. 167 could alsobe EEG (electroencephalogram) lead wires 478 that could be attached tothe patient's head. FIG. 167 is made to be encompassing of anymonitoring leads which could be placed anywhere on or in a patient.

FIG. 133 shows that such external lead wires 478 and electrodes 466described in FIG. 167 are easily protected with the novel distal TIPTANK filter 146 of the present invention. Protection of these types ofexternal lead wires is very important because often patients are sent toanother location for an MRI from a hospital bedroom or other locationwhere they had many FIG. 167 lead wires placed on them. Removal of allof these leads is a very time consuming procedure prior to MRI. Worseyet, after the MRI, the MRI technicians attempt to place these leadwires back in the correct positions, however, MRI technicians oftenreplace them incorrectly. Even a slight difference in where you placethe lead can affect subsequent data. Often the MRI technicians place theEKG leads back in an entirely different position which can lead toerroneous data. This can be very frustrating and confusing forcardiologists, for example, that do not even realize that another doctorin the hospital had sent the patient upstairs to get an MRI. Often whenthe patient is sent back to their hospital room, the cardiologist ispuzzled by differences in cardiac readings that they cannot explain.Accordingly, this is an important application for the novel TANK filterof the present invention.

FIG. 168 is the schematic of the novel tank filter of FIG. 167.

FIG. 169 combines the principles from FIG. 8 and FIG. 17 together.Referring to FIG. 169, one can see the housing 102 of the activeimplantable medical device 100. Contained inside of the activeimplantable medical device are electronic circuit boards 790 throughwhich a lead wire 104 egresses through a insulative hermetic feedthroughterminal 792, including a prior art feedthrough capacitor such as waspreviously illustrated in FIGS. 3, 4, 5, 6 and 7. Lead wire 104 isdirected to the novel TANK filter 146 of the present invention which isimmediately adjacent to the distal TIP 142. Referring back to FIG. 169,this forms an MRI compatible system. In this case, the value of thefeedthrough capacitor must be sufficiently high so as to preclude theentry of the MRI pulsed RF signals into the interior of the AIMD housing102 where such EMI could interfere with the proper operation of thecircuit board 790. As described throughout this invention, the distalTIP TANK 146 acts to stop the flow of MRI currents near or at the distalTIP thereby preventing overheating. Said tanks can also be placed inother locations along the lead wire 104, including immediately adjacentor even inside of the feedthrough capacitor 792 as previously describedin drawings 162-165. Accordingly, one can see that the distal TIP TANK146 of the present invention acts as a system in concert with thepassive feedthrough capacitor low pass filter 792 as illustrated.

Although several embodiments have been described in some detail forpurposes of illustration, various modifications may be made withoutdeparting from the scope and spirit of the invention. Accordingly, theinvention is not to be limited, except as by the appended claims.

What is claimed is:
 1. An implantable medical therapeutic or diagnosticdevice, comprising: an active medical device including electroniccircuitry for therapy delivery or detection of biological signals; alead in electrical communication with the active medical deviceelectronic circuitry; an electrode assembly electrically connected tothe lead; and a tank filter associated with the lead and having aninductor in parallel with a capacitor, wherein the configuration orcomposition of the capacitor's electrode plates are adjusted to raisethe equivalent series resistance of the capacitor such that the tankfilter has an overall circuit Q to attenuate current flow over a rangeof selected frequencies.
 2. The device of claim 1, wherein the overallcircuit Q results in a three dB bandwidth on the order of MHz.
 3. Thedevice of claim 1, wherein the range of frequencies comprises a range ofMRI RF pulsed frequencies.
 4. The device of claim 1, wherein one or moreof the capacitor's electrode plates have a reduced thickness for raisingthe equivalent series resistance of the capacitor.
 5. The device ofclaim 1, wherein one or more of the capacitor's electrode platescomprise a high resistivity electrode material for raising theequivalent series resistance of the capacitor.
 6. The device of claim 1,wherein one or more of the capacitor's electrode plates are comprised ofan electrode ink/dielectric powder composition for raising theequivalent series resistance of the capacitor.
 7. The device of claim 1,wherein one or more of the capacitor's electrode plates are providedwith apertures, gaps, slits or spikes for raising the equivalent seriesresistance of the capacitor.
 8. The device of claim 1, wherein one ormore of the capacitor's electrode plates have a relatively greaterlength than a width, for raising the equivalent series resistance of thecapacitor.
 9. The device of claim 1, wherein the capacitor comprises adielectric material having a high dielectric loss tangent at theattenuated range of frequencies.
 10. The device of claim 1, includingresistive electrical attachment materials for the capacitor, to raisethe equivalent series resistance of the capacitor.
 11. An implantablemedical therapeutic or diagnostic device, comprising: an implantableactive medical device including electronic circuitry for therapydelivery or detection of biological signals; a lead in electricalcommunication with the active medical device electronic circuitry; anelectrode assembly electrically connected to the lead; and a tank filterassociated with the lead and having an inductor in parallel with acapacitor, wherein the configuration or composition of the capacitor'selectrode plates are adjusted to raise the equivalent series resistanceof the capacitor such that the tank filter has an overall circuit Qresulting in a three dB bandwidth on the order of MHz to attenuatecurrent flow over a range of selected MRI RF pulsed frequencies.
 12. Thedevice of claim 11, wherein one or more of the capacitor's electrodeplates have a reduced thickness for raising the equivalent seriesresistance of the capacitor.
 13. The device of claim 11, wherein one ormore of the capacitor's electrode plates comprise a high resistivityelectrode material for raising the equivalent series resistance of thecapacitor.
 14. The device of claim 11, wherein one or more of thecapacitor's electrode plates are comprised of an electrodeink/dielectric powder composition for raising the equivalent seriesresistance of the capacitor.
 15. The device of claim 11, wherein one ormore of the capacitor's electrode plates are provided with apertures,gaps, slits or spikes for raising the equivalent series resistance ofthe capacitor.
 16. The device of claim 11, wherein one or more of thecapacitor's electrode plates have a relatively greater length than awidth, for raising the equivalent series resistance of the capacitor.17. The device of claim 11, wherein the capacitor comprises a dielectricmaterial having a high dielectric loss tangent at the attenuated rangeof frequencies.
 18. The device of claim 11, including resistiveelectrical attachment materials for the capacitor, to raise theequivalent series resistance of the capacitor.